I think your stance on purely flavor/aesthetic form differences like Alcremie, Vivillon, and whatnot largely depends on what you engage in Pokemon for and what you expect from different Pokemon you like best.
If you're mainly interested in Pokemon for the battling aspect, then yeah, you're probably not gonna care much about multiple forms that are purely aesthetic or there for flavor/lore.
But if you're the collector type who loves collecting Pokemon, or you're just deeply interested in worldbuilding and the Pokemon world and are interested in this kind of stuff, then you're probably more likely to like at least some of these mons. People who are purely into Pokemon for collecting may find a lot of fun in collecting these forms and it brings a new fun value in trying to catch and evolve multiple of the exact same species for the sake of their collection. Some other people may just find it cool that one Pokemon can have so many aesthetic differences for a variety of reasons like with the likes of the Flabebe line and the multiple Vivillon forms across the world. Evolving many different Alcremie forms from Milcery through a variety of spins in-game.
The main thing that makes Pokemon so appealing to a wide audience is that everyone has their own reasons for being into Pokemon. This is Smogon, a board of forums focused on competitive Pokemon battling, so naturally a lot of people who frequent here will be into Pokemon for the battling aspect (I myself included admittedly). But there are many who don't see Pokemon battling as the main reason they're into Pokemon, and they may find value in things we as the type who enjoy Pokemon for its battling aspect don't really find value in. Most of us here on these forums may not care much for mons with purely aesthetic form differences like Vivillon, Florges, and Alcremie having these different appearances because they don't affect their battle capabilities, which is the main thing we're into Pokemon for, but some people who just love collecting Pokemon or just like these forms because of worldbuilding may genuinely find merit in these mons and value in collecting them or just them existing.
Some people say "variety is the spice of life", and as cliche as it is, in this case that does apply with Pokemon as a whole in a weird way. There are many kinds of people who can be into Pokemon for different reasons, and all kinds of Pokemon exist in different ways, and as such just about any Pokemon that exists can appeal to all different kinds of people and each individually to different crowds. Even Pokemon that don't seem appealing to many of us here who are into Pokemon for battling can still have merit to other people who enjoy Pokemon for a different reason that isn't the battling aspect. That's why Pokemon has historically appealed to so many people and become so popular worldwide after all.
If you're mainly interested in Pokemon for the battling aspect, then yeah, you're probably not gonna care much about multiple forms that are purely aesthetic or there for flavor/lore.
But if you're the collector type who loves collecting Pokemon, or you're just deeply interested in worldbuilding and the Pokemon world and are interested in this kind of stuff, then you're probably more likely to like at least some of these mons. People who are purely into Pokemon for collecting may find a lot of fun in collecting these forms and it brings a new fun value in trying to catch and evolve multiple of the exact same species for the sake of their collection. Some other people may just find it cool that one Pokemon can have so many aesthetic differences for a variety of reasons like with the likes of the Flabebe line and the multiple Vivillon forms across the world. Evolving many different Alcremie forms from Milcery through a variety of spins in-game.
The main thing that makes Pokemon so appealing to a wide audience is that everyone has their own reasons for being into Pokemon. This is Smogon, a board of forums focused on competitive Pokemon battling, so naturally a lot of people who frequent here will be into Pokemon for the battling aspect (I myself included admittedly). But there are many who don't see Pokemon battling as the main reason they're into Pokemon, and they may find value in things we as the type who enjoy Pokemon for its battling aspect don't really find value in. Most of us here on these forums may not care much for mons with purely aesthetic form differences like Vivillon, Florges, and Alcremie having these different appearances because they don't affect their battle capabilities, which is the main thing we're into Pokemon for, but some people who just love collecting Pokemon or just like these forms because of worldbuilding may genuinely find merit in these mons and value in collecting them or just them existing.
Some people say "variety is the spice of life", and as cliche as it is, in this case that does apply with Pokemon as a whole in a weird way. There are many kinds of people who can be into Pokemon for different reasons, and all kinds of Pokemon exist in different ways, and as such just about any Pokemon that exists can appeal to all different kinds of people and each individually to different crowds. Even Pokemon that don't seem appealing to many of us here who are into Pokemon for battling can still have merit to other people who enjoy Pokemon for a different reason that isn't the battling aspect. That's why Pokemon has historically appealed to so many people and become so popular worldwide after all.