They want the Mythical pokemon to be rare event things where you have a limited . The ones that you CAN obtain have basically been whims:
-Deoxys, ORAS only. Honestly I think the only reason this is here is because they, on a whim, thought that the episode where you break the meteor would be cool if it was Deoxys meteor.
-Magearna, Alola. Honestly I have no idea why they decided you could get one guaranteed by scanning a QR code. Whims!
-Meltan/Melmetal. This is the "Go" pokemon, so it leans hard into the Go mechanics by needing you to obtain a bunch of them to even evolve the stupid thing. For once, not a whim, it operates on pure mechanics while encouraging you to buy Let's Go (and later Home)
-Keldeo, SWSH (w/DLC) only. ngl even having the other swords here feels like a weird whim of fancy.
-Arceus. They wanted to do a fancy game in Sinnoh, Arceus was there as focus. If this had been a "Hoenn" title I suspect it'd have been Rayquaza rather than something like Jirachi. Basically, we got lucky.
-Phione....does this count? I guess it kind of counts. You can get them provided someone, somewhere, has either a Manaphy or Phione. You can blame that squarely on the whim of them wanting an easter egg pokemon.
So the things being hard to get if you miss the event (or, indeed, generation) is a feature not a bug. It's not a problem to them. They want these things in their stable of stuff they can tie to whatever event strikes their fancy. Tanabata give aways, movie give aways, Pokemon center give aways, weird things like the scrap campaigns, join the trainer club to get our newsletters and incorporate yourselves into our ecosystem, participate in this poll, etc etc
it definitely would be nice if every mythic, at least of a generation, got to have a full little in-game quest line to obtain them but that's definitely not happening. It's ingrained into their design to be events and they've moved away from even having notable in-game events for getting them and taking them somewhere for years now.
-Deoxys, ORAS only. Honestly I think the only reason this is here is because they, on a whim, thought that the episode where you break the meteor would be cool if it was Deoxys meteor.
-Magearna, Alola. Honestly I have no idea why they decided you could get one guaranteed by scanning a QR code. Whims!
-Meltan/Melmetal. This is the "Go" pokemon, so it leans hard into the Go mechanics by needing you to obtain a bunch of them to even evolve the stupid thing. For once, not a whim, it operates on pure mechanics while encouraging you to buy Let's Go (and later Home)
-Keldeo, SWSH (w/DLC) only. ngl even having the other swords here feels like a weird whim of fancy.
-Arceus. They wanted to do a fancy game in Sinnoh, Arceus was there as focus. If this had been a "Hoenn" title I suspect it'd have been Rayquaza rather than something like Jirachi. Basically, we got lucky.
-Phione....does this count? I guess it kind of counts. You can get them provided someone, somewhere, has either a Manaphy or Phione. You can blame that squarely on the whim of them wanting an easter egg pokemon.
So the things being hard to get if you miss the event (or, indeed, generation) is a feature not a bug. It's not a problem to them. They want these things in their stable of stuff they can tie to whatever event strikes their fancy. Tanabata give aways, movie give aways, Pokemon center give aways, weird things like the scrap campaigns, join the trainer club to get our newsletters and incorporate yourselves into our ecosystem, participate in this poll, etc etc
it definitely would be nice if every mythic, at least of a generation, got to have a full little in-game quest line to obtain them but that's definitely not happening. It's ingrained into their design to be events and they've moved away from even having notable in-game events for getting them and taking them somewhere for years now.