He must be running low on either money or hope that a third Conor fight is gonna happen soon bc before he was only accepting fights that he got PPV points for (which is why he's been out so long).
I'd bet he knows that with Khabib having the belt he'll be the obvious priority. Probably best to stay somewhat relavant in the UFC so if the trilogy come into play the interest is still there. He got paid well to fight Conor and he's his own academy iirc so he should be doing pretty good. Should be.