While I would also love for more spotlights to be shined on recent Pokemon and have them included in more media, the Kanto pandering is understandable from a marketing perspective and definitely not a uniquely Pokemon "problem." I'd wager that most franchises from 20-30 years that are still active currently are a rehash of their respective "Gen 1," especially in ancillary media. Many of these properties have taken an "expanded universe" approach in which characters from later iterations are included in roles of varying depth and focus, and introduce some original characters, but the stories still primarily focus on the old well-known characters to drawn in people who were familiar with the franchise but haven't been following it. A few examples:
- Transformers: following the original run the series/toyline made a big change and introduced Beast Wars (and the related Beast Machines), in which the transformers took on animal modes (which looked organic and not robotic in "beast mode," unlike, e.g., the Dinobots in Gen 1) which drew from the original series in having many characters named after the originals but otherwise having their own characterizations. Even then, the show did ultimately tie its lore back to the original series. Japan localized the Canadian-produced TV show but also developed its own Beast Wars animes with all new characters. Following the Beast Wars era the toyline pivoted back to vehicle modes and introduced new characters but with new iterations of "Optimus" and "Megatron," as well as some other well-known Gen 1 characters. Following this was Transformers: Energon trilogy which again introduced many new characters and gimmicks but also had iterations of Optimus, Megatron, Starscream, etc. After this it seems like many of the recent stories have been rehash after rehash of the Autobot vs. Decepticon war, often starting with a contrived reason to end up on Earth and interact with squishy humans who prove to be valuable to the Autobots' war effort, but sometimes starting before the war. The most recent Netflix show takes this latter approach while mostly follows the status quo of Optimus-led Autobots vs. Megatron's evil Decepticons, but the next season will introduce Beast Wars characters (who have mostly played side roles in recent media). There was a good run of the IDW comics which, while still focusing on old well-known characters, disrupted the status quo and actually had the war end and explored post-war life, but that run ended and it sounds like the new run is back to rehashing the "leading up to the war" era again.
- Power Rangers: while it seems like the Power Rangers TV show has continued to introduce brand new characters every season, with occasional connections to earlier seasons, other media is predominantly based on the original Power Rangers in an expanded universe setting. The TV show is perhaps then most analogous to the games, with the format mostly staying the same (a team of rangers with Zords versus monsters of the week ~ 8 challenges, evil team, become champion) with new characters and powers (~ new pokemon). The current run of the comics appears to have two branches, one based on the 2nd season squad of Power Rangers with some OC as the Green Ranger vs. the original villains and another based on the original Red, Yellow, and Black ranger off in space on a mission (with an alternate universe evil deposed dictator version of Tommy). In the previous series set in the same continuity before these two launched there was a multiverse-type thing in which Power Rangers from other TV seasons appeared, but I don't know if any have shown up in the current run. There was apparently also a video game based on this multiverse run of the comics.
- Digimon: Youtube keeps trying to recommend me clips of some new Digimon show that is based on the original characters, and to the extent that I've watched any of them it's only because I recognize the characters. My familiarity with anything passed the... 4th season? The one where they finally went "screw it, just make the humans turn into Digimon," is negligible.
I'm sure there are more examples as well. In all of these cases I have to admit I would be unlikely to watch a video or check out the comics if it weren't for Gen 1 familiarity, and I imagine that that is true for many people that are casual fans of a franchise. More dedicated fans want new novel content*, but getting returning eyes on the franchise, especially offshoots, usually requires a focus on the old familiar characters perhaps with new designs/powers. Even when it seems like this doesn't make sense for some products like Smile, which would be for kids who don't even have this familiarity, the goal is to get the parents' attention and give them an angle that they can use to connect with their kids. The Kanto pandering is something that I think the Pokemon community just has to make peace with, since it doesn't seem like it will be going away anytime soon.
(*An exception to this seems to be a certain clade of Transformers fans who appear to only want TF media to be a continuation of the original cartoon universe in perpetuity)
While fans from Japan have more love toward Gen 5, there is also a massive hypocrisy about the overall fanbase whereas they don’t like the excessive Gen 1 pandering and yet let slide fan projects that are just Kanto and nothing more, despite these project having an even more varied quality than even the official mainline Pokémon games.
Another and more important thing, is that there are major differences between Pokémon and the other franchsies with massive pandering of Gen 1 of how they do it.
The other three franchises are simply retellings or even entirely new stories for the most parts, despite some common well-known patterns. This allows new interpretations and fresh new takes on the franchises. Aside of Detective Pikachu, Pokémon Ranger and Pokémon Mystery Dungeon, and to an extent Pokken and the many manga lines of the Pokémon franchises, the many other spin offs only stray a bit from the traditional formula of the Pokémon as a whole beyond distinct gameplay.
Another difference is how they handle new additions, often done to help make the next iteration stands out to various extent of success. I am not in a position of judging the new additions of Digimon, Power Ranger and Transformer, but I believe the Digimon franchise avoids giving buff to already strong and popular Digimon, something that Pokémon is very guilty of giving Mega Evolution to Pokémon that are already strong and popular, and ends up being overpowered.
Pokémon tend to go overboard with Pokémon that proved to be popular, as seen with the Kanto starters (with the Charmender line being the biggest culprit of the three), Gengar, Greninja, Lucario, but especially Pikachu, and while the franchise as a whole is not the only culprit for sure, it is very obvious that they focused way too much on marketing lately to the point that it ended up hurting the quality of certain things.
One of the reasons why people eventually make peace with Alolan forms being Gen 1 only is that most of the orignal form of the following Pokémon are not popular to begin with or are severely overshadowed, which include but not limited to the Geodude line, Raichu, Exeggutor, Marowak, Grimer line and the Ratatta line. In short, it focused on those that are not the most popular Pokémon out there. It helped that this aspect is continued to the Galarian forms in Sword and Shield, expending to Generations beyond Gen 1 this time.
Same cannot be said with Gigantamax forms, which the distribution feels not only unnatural, but also something that felt slapped on instead of something that is organic with Galar as a whole. They also barely more rewarding than capturing a Dynamax Pokémon in a Max Raid despite the chance of missing the capture, because the G-Max Moves are not always better than their standard counterpart of the same Max Move type... if not worse. They don’t even change Abilities! (Not necessary for Urshifu.)
tl;dr Pokémon focused too much on marketing to the point that the pandering ends up coming off as insincere.