>>123755351) having too many could just become a logistical nightmare. You'd have trouble keeping track of them all, for instance.
2) No matter how creative your ideas/designs are, you'll have to reach a point where you run out and start repeating the same old designs over and over again. Hell, in some respects we're already doing that (gigalith and swoobat lines just being knockoffs of golem and crobat lines, respectively).
3) And in order to try to make all these new pokemon different from previous ones in terms of battle usage (which becomes exponentially harder as more are added), you'll simply run out of "roles." And then the only way to differentiate is to have THIS pokemon be exactly the same functionally as THAT pokemon, but BETTER. ie, power creep. And over many generations, this will just become ridiculous.
