>>37540804because the other series have been created from the start around the pretense of different standards. you see 1-5 monsters in those games, you pretty much know what you're generally getting yourself into with everything else. like you said, the other series get away with going hog wild and making designs based on whatever the fuck they feel like. the presence of such things has likely been established early on, be it through existing designs or the game's overall tone, including them as a part of the inherent standards of what those games' monsters should be like. meanwhile, the chronology of pokemon's generations, and comparison of designs along that chronology, are more distinct because of the different pretense that the earlier generations set. regardless of what you do or don't enjoy from each generation, you can't deny that general design can be quite different between the generations. this then leads to discontent based on your own preferences.
not to mention that more emphasis is placed on pokemons' designs based on how long the specific designs typically exist in a player's party, as well as how general design choices are usually preserved through an evolutionary line. compared to something like digimon, you're going to be playing with and "nurturing" these designs for a longer time while looking forward to how the general design of the thing develops as it grows, and so it's more of an overall investment. it's the combination of that development of a design and the consistency with which that design is present throughout one's experience with it. as far as I can tell, most people are less satisfied using mons that only evolve once or don't do so at all. one can also compare it to digimon in this way, as its designs throughout digivolution lines are notorious for drastic shifts. if you like or don't like whatever thing your digimon is at the moment, it doesn't really matter, because it can be a completely different thing the next moment.