When one side thinks there is no chance in hell they could win, that attracts a lot less viewers, however it is still not a lost cause as a viewer for many people, because they are trying to get something out of it. What could they possibly get? Well for a Mayweather fight I think nothing, normally I would assume that in a regular boxer vs youtuber situation we would be expecting boxer to beat the hell out of the youtuber, and that is actually kind of the point, you could spend money to watch mayweather beat logan, and that ain't really the worst thing I would spend money on.
Plus, the PPV price could be lower on this, I didn't hear what it will be like, if it is really cheap and we have corona everyone, so you could just get couple beers and a pop corn and watch mayweather beat the hell out of two moronic brothers. That ought to worth something in the end

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Normally I would agree with you that there would be less viewers for a known outcome, but in this case I think everyone is paying to see Logan get knocked out. I can't remember the last time I saw Mayweather knock someone out, as his last several fights have mostly been him dancing around earning technical points, so I think he actually has a bit to lose in this event. If he can't even knock out Logan Paul at this point in his career, why would anyone still pay to see him fight? For example, do you think there's any chance in hell Mike Tyson wouldn't knock Logan Paul out? Why isn't Mike the one getting tens of millions of dollars to knock out youtubers?