Anyone who have followed Gus over the years should be able to read through the lines here.
Gus is an elite fighter in a severely damaged and shallow division. As an athlete in his position, it's dumb to just fight "anyone, anytime", especially when he's the no.1 contender in his division. What options does he really have at 205 that gives him the money/recognition he deserves?
He has already fought most of the fighters in the top 10, and the rest is either booked or part of his camp (Latifi & Manuwa). He's actually in a pretty rough spot, which kinda reveals itself when he desperately tries to talk smack.
With that said, he should really pursue the fight with Rockhold. It's a relatively big name and very winnable.