>>49182395i do it because my language uses the grammatical gender, we have feminine, masculine and neuter, so we refer to things like closet and flower as 'she' and table as 'he' etc.
so it's natural for me to refer to pokemon as he or she and i have a habit of translating that into English although that don't make much sense then, but oh well force of habit. I also refer to them as 'it' as well of course.
Funny thing though, Jigglypuff sounds like a masculine noun to us so I'm used to calling it 'he/him' and it feels very weird when people call it 'she' (mostly people playing Smash)
We also inflect the pokemon names so for Jigglypuff it can change to forms like Jigglipuffa, Jigglypuffovi, Jigglypafem etc. acording to the declension for the masculine gender.
Maybe someone'll find this interesting but it's probably just rambling.