The same reason why people are customers of TicketMaster, BofA, Comcast, or many of the companies competing for Worst Company in America: While EA doesn't have a whole monopoly on their market, they are an unignorable player.

People hate TicketMaster but they aren't willing to forego a concert to voice their opinion. People hate BofA but they don't know about the great alternatives they have in credit unions. People hate comcast, but sometimes it's the only ISP available. Similarly, EA touches on all of these fronts.