I think things like weight are cyclical similar to fashion. They go in and out of season. I think up to 70s, curvy women was the trend. Around 90s, skinny women were popular. Some were even anorexics. From the 2000s to the present, big butts and bigger women are popular. What's funny is if you watch the music video of Baby Got Back, the women depicted there are normal/thin by today's standards. The "big butts" there are small compared to the big butts of today.