LeBron is no different. He's just a Tim Tebow at a much higher level. He's about as big as stars get in the US, a card with him on would sell 4+ million PPVs from the novelty factor alone, and at that level he could easily get well over 100 million. Forbes listed him as worth 275 million in 2016, he's probably worth around Dana White's level now (400 million), and 100 million to LBJ is a significant amount of money.
These one off fights would benefit most celebs, unless if you're sitting on billions, which most celebrities arent.