"I remember being a teenager/early 20s and thinking "omg these women who let themselves go, how do they live like that?" (aka without appearance-based validation), but now I look at teenagers/women in their early 20s and think "omg these girls and woman who obsess over their image, fashion, etc. how do they live like that??""
EXACTLY. I will still put on some make up and efforty clothes at times, but generally, I just don't care if anyone finds me attractive these days, except my husband.
OP, at your age, I was still going out clubbing, pulling every weekend, dressed up to the nines.
Guys aren't looking at you because you're not looking at them. If you did, they'd look. Probably lack of confidence. But if you have a husband, why do you even want other men's validation?
If no one cares about your opinion, that's something totally different.
Work on your confidence. Your life being effectively over at 30 is a really sad and desperate way to look at things.