For exhibitions matches, it's usually retired MMA fighter so yeah, probably just another way to make a living after hanging your gloves in the professional ranks. So it is still very lucrative for them and then the Paul brothers pushes the boundaries like the last one when it was reported that Mike Tyson gets $20 million and Jake Paul $40 million.
Actually, even active MMA fighters (not just retired ones) are choosing to leave MMA and move to boxing because that’s where the big money is.
Conor McGregor is the most famous example, he made a fortune from boxing. But another one that comes to mind is Francis Ngannou, he was an MMA champion, but he chose to step into the boxing ring against a boxing champion, and that decision earned him a massive payday.
https://www.thescottishsun.co.uk/sport/13703247/francis-ngannou-borrowing-money-mma-boxing/He walked out on the UFC as their heavyweight champion to pursue a his lifelong ambition of boxing.
At the time, he had beaten Ciryl Gane in January 2022 but had no plans to re-sign with the UFC.
He made only £450,000 for the bout and revealed he borrowed £150,000 from friend and former UFC champ Kamaru Usman.
But after two boxing bouts - against Tyson Fury and Anthony Joshua - he is believed to have earned over £10MILLION.
If I'm not mistaken, Francis says that he didn't feel anything from Dana, perhaps we was not a favorite and so they didn't extend his contract. And if by chance they offered it, they low ball him that's why he decided to leave for good. And it did pay off as he had a boxing fight with two of the best heavyweights and earning career payday for him. However, for others it might not be the case and they go on some low level organization just to earn in the sports of MMA.
So good for Ngannou, and so he is back to the MMA again and really still fighting and not might getting the money he got from fighting, at least he has a career and hopefully he will used that money in the right way, just saying. So we can say that not everyone has a good chance to make a lot of money if they go out of UFC.