>>38014945Digimon and SMT have been going on for ages and they don't maintain all the monsters between entries.
Fighting games work on a similar principle of the characters being a draw like Pokemon are and Smash Ultimate is the only case of one maintaining all of them (and that's just that once, not even consistently).
It's by no means a norm or a standard or an expectation to never drop features or characters or faction or mechanics as a series grows. In fact the rare few sequels that have full parity with the first and only grow from there are incredibly Rare.
The logistics involve in implementing and maintaining the sheer number of Pokemon is what is killing this series.