>>58306568It's a mix of two design philosophies. The first being that every area had to have at least 1 new Pokemon (usually 2), so naturally there were gonna be Pokemon that appear late, combined with the fact that every Pokemon has at least 10 levels before they evolve from the moment you catch them to ensure you spend some time with that stage before they're gone.
Which is perfectly understandable because, if you ask me, I'd rather have a late evolution than retarded shit like the Jangmo-o situation where you literally evolve twice in two levels because it's already at its full requirement by the time you find one.