Quoted By:
The thing is that in the west the "Playboy Bunny" outfit is... the Playboy Bunny outfit, which is directly related to pornography.
In Japan, the "Playboy Bunny" outfit is just seen as "bunny outfit", kinda sexy but not inherently porn, in the same way that Jenny wears a "police outfit" that has a miniskirt and high heels, or maid outfits that have been featured in some episodes of the anime. Or you know, swimsuits. Bunny outfits appear in a lot of shonen manga and also appear in a nearly every Dragon Quest games, a series that is just as mainstream as Pokemon in Japan and is considered perfectly appropriate for young children. Picture related, a Dragon Quest 11 party member wearing a bunny outfit costume. That game is rated Cero A in Japan, which is the equivalent of the ESRB "Everyone" rating.
tl;dr Lopunny is likely based on a bunny outfit but that outfit does not have the same connotation in Japan, still sexy but not inherently pornographic.