It is though.
There is a reason new Generation(with new Pokemon) always sell better than Remakes, even though remakes usualy have more/refined features.
There has never been a pokemon game that allowed you to catch all pokemon anyway, not even gen 1(no mew without hacking/events).
They can keep the number aviable around 500, and just rotate the aviable ones for each game.
Technically it is not an issue either, irc from a Pokemon Go datamine we know all pokemon models in 3D are about 1GB in total.
So even if we double or tripple that to 2000+ we would only be around 3Gb, which is nothing when switch cardriges can be up to 64 GB.