- Game Freak doesn't have to be beholden to all literally a thousand Pokémon that came over the last twenty-seven years before when designing new items and mechanics. A classic example is Tera-Electric, Air Balloon Shedinja - They don't have to make seasonal mechanics like tera work around weirdoes that could exploit them too easily.
- In addition, the shifting roster allows more Pokémon time to shine in competitive. Pokémon that'd be bullied out of taking a spot have a better chance of finding a niche if there's less alts to compete with for the spots.
- The big fear of Pokémon getting trapped in Home forever isn't bearing out in practice. The rosters in Gen 8 and 9 have overlap, but enough unique ones on either side that most Pokémon have gotten at least some chance to shine in a mainline game on switch. According to @Nick Gars in
this very thread, the only ones who haven't appeared yet are Spinda, Furfrou, and Gen 5 Pokemon who are likely to appear in the inevitable Gen 5 remake games.
- The rule is literally something only Pokémon did regularly. Mon and mon-related games with far smaller total rosters chickened out far faster than Pokémon did, if they ever tried to keep to that rule at all. And they certainly never allow you to keep and transfer your Pokémon across games.
- People complaining about animation quality and variety don't acknowledge that Pokémon does things in the animation department that literally no other series does - most of which could be argued as stupid, or at least inefficient. See
a previous post for more details. They don't do recolours in the traditional sense - even regional variants and fakes have their own models and animations. And likewise, they avoid the Agi-Agilao-Agidyne rule of just making the exact same moves but stronger.
People say that to be a good mon game, they should animate all the punch moves as punches and all the kick moves as kicks, without acknowledging that the games they're comparing to don't have that problem because they don't have the move variety to separate that stuff from each other.