He's the one that "offered" to fight Usyk. However, that "offer" was for a disgraceful 70/30 split. Usyk would've only gotten 30% of the purse but he did the unthinkable and actually accepted. Fury then decided to play games and showed that he never intended to be ready for their fight date (which had already been rescheduled for a second time). He had his bluff called in front of the world for all to see.
Sure, he can fight nobodies and still make good money and apparently that's what he'd rather do now. Hence a large portion of his fanbase abandoning him. He has no interest in proving that he was ever the best in the division. It will reflect very poorly on his legacy. The guy had a chance to prove that he's the top heavyweight of his era. You know, mega money fights, all the titles, and all the fame that comes with it. He's pissed it all away.