consider the things you're considering.
I find no evidence anywhere that these donors aren't also very concerned about other charitable causes.
How many donors to BYU sports do you think have given $100k or more and the donation to BYU sports are their only donations? I'll bet the number is exactly zero. And... I'd be willing to bet that of these donors the amount they give to BYU sports is less than 10% of their total giving.
Additionally... having strong BYU sports helps the church. So donating has a duel impact (helps our hobby, helps the church).