AJ went into the first bout as unified champ - rematch clause wasn't really so unreasonable. And AJ 2 was a more competitive bout than Fury 2. Dubois... I didn't think the first was particularly competitive - Dubois only had lowblows and the ref wasn't falling for it, but some people fell for it and whipped up controversy where none should've existed. That and Dubois still being young and appearing to have made progress made it at least interesting - it turned out to be even more one-sided than the first, but he at least deserved it more than any other options available at the time. None of this applies to Wilder - he's not a champion, he won't be competitive at all, and he's not getting better.
Wilder already did that against tomato cans. Once he stepped up, the gimmick ended. Same for Andy Ruiz. His gimmick was that nobody took him serious and he was in better shape than his body looked. No fighter made that mistake again and Andy never came into a fight in good shape again...although his body actually began looking better which is the irony.
Both of their first fights weren't remotely competitive and didn't warrant a rematch. It didn't stop Usyk from doing so, and remember her was even open to fighting AJ a third time. The first Fury fight was very close and competitive and deserved a rematch. Why people continue to make excuses for Usyk is beyond me. It's a shameful fight for a unified champion to make.
Dubois wasn't remotely competitive... Joshua's first effort wasn't really competitive, but it wasn't as bad as Dubois effort. Usyk had no choice with Joshua - it would've been a clause in the contract, and again when you're talking about a 3-belt unified champ in particular that isn't especially unreasonable. As for a third... Joshua did much better second time around - still lost fair and square, but you could still argue more interesting for a third bout than Fury who was at times was competitive first time (but should still have been a clear UD) and wasn't really second time. Dubois 2? Up to a point - if only to shut up the nonsense about the lowblows. Wilder? Complete waste of time, shouldn't have been made - better current options available by far.
This. But, if Usyk did decide to go down from a shot, he had better make sure it's from a jab or something LOL.