That was easy. The biggest question mark surrounding this fight is how so many people were convinced McGregor has enough of a chance to win that they were willing to put money on it.
It made some sense under the original odds; at +950 for McGregor and -2000 or worse for Mayweather, it was hardly worth betting on Floyd at all. The ROI at -2000 in a fight where the other guy has a puncher's chance is complete shit. So anyone who felt a burning need to put money down were only incentivized to bet on McGregor. What the hell, right? If I have fifty bucks I don't need and a miracle might turn it into $500, and I have the chance to say I believed in McGregor enough to put that money down if he does somehow win, it might be worth taking a flyer on it. Thus the movement of the betting line towards McGregor was inevitable.
The extent to which that's the case is a different story. One week before the fight, Mayweather's down to a -450 favorite, with McGregor at +325. A +950 line means approximately 10:1 odds; McGregor has to have at least a 10% chance of winning the fight to make the bet break-even. To give McGregor that much of a chance against the greatest boxer of the last two decades is a hell of a stretch at best, but those are the best odds you'll get, so jump on them when you can. Pretty quickly, however, only stupid money follows the semi-smart. At what point is a McGregor bet clearly a losing proposition, no matter your belief in his youth and the hope his striking power can translate to boxing? +700? +500? What argument can support McGregor having a legitimate one in five chance of beating Floyd goddamned Mayweather?
More over, when does Mayweather start becoming worth the money? Or when did he, since he clearly is at this point? Right now, you'd have to put down $450 to win $100. It's still mainly a bet for serious gamblers, the ones who place enough bets to withstand the variance of surprise outcomes; it's harder to justify risking $450 per $100 profit on a one-off. That doesn't change the fact that Mayweather, at these odds, is an incredibly good value.
Here's part of an overheard conversation about the fight: "If McGregor goes twelve rounds with Mayweather, that's going to prove MMA is for real. It'll be huge for the sport." That guy could end up being right, but if he is it won't have anything to do with McGregor proving something about his sport by going the distance. It will be McGregor and Dana White cranking the hype machine up to thirteen letting people know what an accomplishment it was to last twelve rounds with the greatest boxer of his generation.
On any logical level, though, that's absurd. Why shouldn't we expect McGregor to last twelve rounds? Have all the people predicting a Mayweather knockout because his skill level is so much higher forgotten his last knockout (apart from Victor 'Gimme A Hug' Ortiz) came against Ricky Hatton in 2007?
If anything, a Mayweather KO would logically prove how different boxing and MMA are. Conor McGregor is an extremely high-level combat sports athlete with fitness to match, facing a man whose greatness is predicated on defense and counter-punching, and who has never shown any qualms about taking zero chances in pursuit of a victory. People talk about what McGregor has to do to knockout Mayweather, which makes sense given that it's his only reasonable route to victory.
Floyd Mayweather doesn't fight for knockouts, he fights for victories. He's an all-time great fighting a well-honed athlete who brings, at best, a low-level professional's skill set in this sport. The most likely outcome, given the track records of the fighters, is that Mayweather scoots around the ring for twelve rounds and McGregor is lucky to land fifty punches of any type all fight. The fact most predictions seem to revolve around a KO for one man or the other defies all logic.
And that's why Conor McGregor is, by the betting line, considered more likely to beat Floyd Mayweather than Marcos fucking Maidana was in the second Mayweather/Maidana fight. People are just goddamned silly.