I don't care for either, but with the sports, it's not about the personality of the athlete, it's about the one game they play. With let's-players it's more or less their charisma that matters, not what they're playing. There are an overwhelming amount of charmless, unoriginal let's-players because it's disregarded as something that any moron with a webcam and fraps can do. And they do. In football, they have talent scouts, training regimens, etc. to try to make the content of their spectator sport worth watching. Unless of course you're the Faroe Islands or FC Svendborg.
So I think it comes down to a matter of oversaturation. You can't do anything on the internet without being redirected to some youtuber or ponies or undertale or five nights at money-grubbing, which is where we draw the line between "annoying" and "cancer"
I'm on a tangent, but hopefully that made sense.