I found a site with some definitional language. If I read it correctly revenue can include donor support as well as support from government sources as well as student fees for athletics. So state schools may derive revenue there. I also recall that Rutgers, for example, charges all students a mandatory (?) athletics fee.
So this seems to be a measure of where each athletic program gets all of its money, by category, not a proxy for popularity or profitability . Not sure where NIL comes in if at all.