I've been thinking this for some time, especially in the wake of NIL, and I don't think it's either a mystery or a surprise. The reality is that the money and exposure of college athletics, and the investment of college donors and fans, far outstrips the WNBA's resources. And while some continue to bash the schools for not sharing this or giving that, the reality is that almost eveything the schools make in profit is reinvested into the system, through facilities, marketing, treatment, and support staff (and also scholarhips for other sports). Once upon a time, it was frowned up to think of playing players, so the schools competed the only way they could - building lavish support systems and beyond first class experiences for their student-athletes. (This also spilled over into coaching salaries, but even coaches are, at a fundamental level, just another benefit schools obtain to improve their team's odds of success).
Nutritional needs? Totally covered, and far better than average students. Tutoring and scholarship? You'll get every sort of help the school can afford under the sun. Place to live? You'll get that too. College education? Free of charge. The schools don't hoard any of that cash away, they take it in, turn around, and spend it on the sports programs.
Now you take all those things, and add the ability to get even some money through NIL? Even if it's only a small amount per month? You're probably far, far ahead of whatever the WNBA can afford. And that's not going to change, I don't think.