Because that's mostly what it get applied to, but as I mentioned in my previous post, I'm against it for any such purposes. In games localized for Japan, it tends to be excessive violence. I'm against that too (though I guess I'd be okay with adding the option to tone things down for people bothered by some of that stuff, since that wouldn't remove it for everyone who played) but it doesn't get talked about much among English speakers because, well, it doesn't affect them. One non-sexualization thing that comes to mind is a change to FF6 in the GBA re-release, however, that change was not done in localization, it was done to the JP release and then we got stuck with it too.
And that kinda gets to the heart of the issue for me. Self-censorship, to the extent it makes any sense at all, is things like the Skull Girls (I think?) pantyshot update. The creators decided it wasn't appropriate and changed it. I'm not okay with that kind of thing if it's, say, removing a scene from a movie entirely and making sure no one can ever see it (at least include it as an extra). But slightly changing a character model? At least in that situation, sure, whatever. But.... that's not quite what's happening here. The JP version HAS NOT CHANGED. This isn't the original creators having some epiphany about some negative aspect of their product or something. This is a *localization* change. It is a change, strictly removing content and options, for only the localization, for some fear or offending people in a different region. And I'm not sure if it's better or worse that it's entirely optional stuff, stuff nobody that would be bothered by it would ever have to see if they didn't want to.
And, like, I can sooort of understand why people have started to read "censorship" as being implicitly about the government, since for years idiots have whined about free speech and/or their first amendment rights for a billion things that had nothing to do with those. But that is not the only thing "censorship" gets used for, nor is it implicit in the use of the word or the only time it's wrong or can or should be objected to.