Why does Comcast force you to use their DNS servers?

It's honestly insane. I'm so bummed to be in a Comcast only building. Between the forced DNS, the limit of 35Mbps (which every Comcast agent promises me is more than enough because they totally understand my specific needs), and the worst customer service I've ever experienced, I'm so miserable using this terrible service. I can't wait for Starry to come to my building so I can drop all this garbage.