I can't imagine a single wealthy person that wouldn't take a cold call from Gates and probably at least agree to a sit down meeting on the spot. Epstein was virtually anonymous relative to Gates.
Given the value of the Bill & Melinda Gates Foundation, why would Gates spend any of his own valuable personal time networking to raise more money for it and not trying to put more of the existing money to work?
Seems like the opportunity cost of fundraising is high.