I stand by the word "unethical", but you can think of it as "shameless" if you prefer.
You are absolutely correct that no PE firm would be interested in "investing in a school's athletic department or conference".
They will have their eyes on all of a school's revenue streams. The biggest of those being annual tuition receipts.
The idea of investors valuing a school's AD is a sales pitch to get their feet in the door. When the final deal is cut, there is no chance the PE's skim will be limited to football revenues or student fees.
Also, I'm pretty sure you get this. I think you are pretending not to understand what's in it for PE's motivation in order to trigger more polemics. I'll keep going if you like, LOL