"Nobody is waterboarding the money down their throat. They can say no. The actual question is: why don't they?"

Leaving aside that metaphor, the obvious answer is that they either like or need it. Most likely the former, because many of these well known universities are swimming in money already.

Why would they not accept money to do something they are interested in doing?

What is the downside to the school of a nicer student union or a public policy/international relations campus in the nation's capital?