Naturally fit folks who've never struggled often think it's because they're better than obese people with self control, and that bigger folks are lazy gluttons. GLP-1s even things out somewhat, and many resent that.
Yep, it's fatphobia at the root. Stay heavy and we're called lazy gluttons who aren't trying enough. Use a GLP-1 and we're lazy for taking a shortcut. No way to win.