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?
Do you remember the last time Floyd Mayweather knocked out a fighter it was in 2011 against Victor Ortiz who was not ready for the fight after referee interference and Mayweather took that as a chance and knocked him out and in my view it was a cheap shot as Ortiz was not ready as he was apologizing for the foul he earlier committed. I can bet that Mayweather will not knockout Logan Paul but he will win on points.
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?
Mike Tyson was known for his heavy hands and Logan Paul nor any causal boxers stand a chance even against an old Tyson as one shot from him will floor anyone.