Debt-holders don't control a company either. But when you have somebody's money and the expectation you are going to give them a lot more money in return, it changes things.
You're correct that they haven't lost control, but now they have somebody to answer to. Somebody who just gave them $100m. Somebody with more equity than all but a few of the people involved. Somebody who's powerful and respected and whose job is to push tech companies in the direction of maximum return.