As usual, the MSM is several years (decades, centuries) behind reality.

Women have always liked a muscular butt on guys. Especially if you hang around female athletes (as I've done my whole life and I'm 59) you heard this across the board. Athletes are all about their bodies, and young athletes full of hormones and looking for status are even more about how their bodies look.

Social Media and a huge number of women posting has lead this old common knowledge to being reported in the MSM as a "new trend." LOL

In meme format:

Noone ever: "A flat butt is really sexy."

Go on youtube and you'll find a video from every major fitness youtuber telling you the exercises you need as a guy to get a round butt.

The #1 best exercise for a round butt is to really (and I mean really) take the time and effort to pick your parents well. That is half the work right there. You're welcome.