Probably someone who's alredy rich, was already going to get paid a fortune for the fight, and stood to profit more from a win. Also anyone who knows that taking a dive is illeagal and can have some pretty serious reprecussions up to and including prison time. Someone who doesn't know how to launder millions of dollars or how they'd explain it on their taxes.
This "take a dive and get millions" tinfoil hat stuff seems a lot more plausible until you have to actually think about how you'd pull it off. Do they give you a nice tracable check or a Walter White-esque pile of cash? What do you do with a pile of cash. You can't go to the bank with it. It's high risk and difficult to spend.
Also how does Endeavor media (UFC's parent company) hide this 5 mil on their books. They explored an IPO in 2019 and are talking about an offering in 2020. Which means their books will be open to high levels of scrutiny. I'm sure they'd be eager to blow a billion dollar IPO on a fight fixing/bribery scandal because Conor's comback could make them tens of millions. Conor is big business in the MMA game, but he's not top 10 on Endeavor's list of concerns.
How to people think all of this works? Do you think millions disappear and no one ever looks where it goes?