It's due to the fact that building a decent network for residential customers at scale is very expensive and not that profitable unless you have a long-term monopoly.
And the people with the long term monopolies want to keep it that way.
Ding ding ding! This is exactly it. As a Google Fiber customer in Austin, it honestly wasn't any better than any of the other ISPs. Ironically, the only thing that was better was the DVR and live TV search that came with the TV service.