Because it's "empowering" to go against the "societal beauty standards of the patriarchy".  Women who take pride in how they look have "internalised misogyny"... or something.  (Seriously, I am with you there, I don't get it either XD) In reality they just can't admit that they are responsible for their shitty life choices and disgusting fat bodies.  Rather than have a modicum of self-care, self-control and responsibility for oneself, they'd rather try and gaslight everyone else in believing they are actually the morally superior and beautiful ones because they don't care about how they look.