Because the cable cartel hasn’t proof what a lack of competition can do. Google had to come with his idea of Google fiber to push other ISP to do something about it.
Corporations are not Saints, if they get bigger and powerful, they will just stand there and suck from the old cow. Just like the deal between AT&T and Time Warner which the only goal is to secure content for cable in a way to slow down the progress of services like Netflix. They do not innovate, just buy time with mergers and acquisitions.