This is in line with SMV theory. Less supply of healthy women increases the value of them and warps the SMP. Average Men who can't compete to get average foids, lower their standards and skew the market for low value fat women... etc. fat women get hit on endlessly and many have big egos now too.
The other reason, IMO, is the rise of the internet. It used to be the only attention and validation a fat woman got was what happened in real life, who she approached. Now any fat woman can have 100 guys line up to hit on her in between tinder, OK cupid, POF, Facebook, etc. So their standards go up, and now fat women think they are drowning in options so they hold out for the top 40 to 50% of men, while the fit and average girls hold out for top 20% / 10%. It is a downward spiral.