They weren't really anonymous. Those who needed to know, knew. The details were just hidden from the general public.

"Really anonymous" might be to set up a trust, interact through a lawyer, where MIT receives no information about the person behind the scenes.

But people at MIT knew, and it helped him make connections with other people.

In addition, the donations were reciprocated. One example (going from memory, so might have details wrong) was that one of the labs was asked to make a gift for Epstein.

It allowed Epstein to launder his reputation as a sexual predator and trafficker. Even with his donations recorded as "anonymous", he remained a conduit and effective networker for the Media Lab. Bill Gates donated $2,000,000, IIRC, to the Media Lab through Epstein. As part of his continued networking as a big dollar donor, Epstein continued using his private island to abuse and traffic underage women.

Basically, once his reputation was in tatters following his conviction, the Media Lab and various individuals found it profitable to rent their reputations (and MIT's) to Epstein.

> “Have you managed to talk to many of my friends?”

> Epstein had been supplying me the phone numbers of important scientists and financiers and media figures. “Do you understand what an extraordinary group of people they are, what they have accomplished in their fields?"

-- http://nymag.com/news/features/41826/

The same reason that you don't do business with organized crime.