Clearly, quite a few characters in the Pokemon universe(s) do name, or give nicknames to, their Pokemon. However, a wide majority do not. To me, it seems that keeping a Pokemon's name to be that of its call/species is akin to calling a dog "Woof" or "German Shepherd". Why don't more trainers name their Pokemon?
I'm hoping to find an in-universe (whichever one you can find one in) answer. But feel free to post fan theories or statements from Nintendo execs as well. I've tried searching for an answer and can find nothing anywhere.