What disrespect are you even talking about? He got offered almost everything he wanted. Got two title shots, they let him hold the belt for a year without fighting, and they offered him a ton of money.
The UFC put an interim HW title fight between Gane and Lewis in August when Ngannou wanted to defend in September after fighting in March four or so months ago. After Gane won and the the undisputed title fight was booked, it could be said they set up Ngannou to lose, or at least they'd hope due to the style matchup. That is speculative to be honest.
What isn't speculative, is after Ngannou beat Gane (late fight wrestling gameplan notwithstanding), Dana White got pissed and ran to the back of the venue to avoid putting the belt on Ngannou, and with no legitimate excuse for doing so at all. They didn't strip the belt from Ngannou because the UFC thought they could negotiate him to stay at their price, but as we know that's not the case.
Ngannou was to be the highest paid of any UFC HW ever (which, being UFC HW champion in 2023, I would hope so) but I find it hard to believe they would pay Ngannou the same or more as Brock Lesnar used to makr per fight. My guess is 1 or 1.5 mill per fight flat no show/win, but probably Ngannou didn't like the number and bounced.
I think it's kind of silly to leave the UFC to go do boxing while that's all the rage, but what isn't silly is refusing to let the UFC low-ball you after arguably disrespecting you and probably prefering you weren't even champ due to you just wanting a bigger cut they can definitely give afford to give. He'll always be remembered for standing up to Dana and the UFC for better or for worse, and I respect that compared to all the asskissing other fighters do to Dana begging for more bonus money because they're on a shit contract. It's unprecedented for any major combat sports org to actually let their HW champ walk, but here we are.