People complain because he is constantly chasing the biggest payday instead of defending his title. if he hunkers down at LW and gets a few defenses, there is nothing left to prove or complain about.
Sure, there are unreasonable that will never like him or be satisfied, but that's just how brains work. there are always idiots that can't find their own nose.
That said, it's not unreasonable to be annoyed by a fighter that gets a belt, hold up a division while he picks his fights, then goes up a division and has his old belt wrongfully held just long enough for him to "break a record" by getting a belt the division up from one of the weakest champs it's ever had, then prance off to an entirely different sport to cash in on his bogus fame instead of defending.