Coaches because they generate tons of revenue.
Doesn't make sense to spend that kind of money for coaches of non-revenue generating sports. I doubt many P5 volleyball programs make more money than BYU ( or lose less). Just because a P5 School makes a ton of money off football doesn't mean it is allocated to other sports.
SEC dominates P5 revenue yet their women's volleyball teams have never won a title. And only Florida has ever been a runner up. By contrast Pacific has two titles and Long Beach State has Three.
Schools with strong academics like Stanford, have a greater advantage over schools with greater athletic budgets because the greatest value most top volleyball recruits are getting is the education.