> One other reason is that counties have the land rights. They negotiate with the big Telco's like Comcast, Verizon, Cox, Charter, etc and then issue a monopoly or duopoly in the county for a fixed period of time - usually 10 years at once.

They do not do that. It's illegal under federal law. Pole and conduit owners are required to rent out access at non-discriminatory rates: https://www.law.cornell.edu/uscode/text/47/224.

The reason companies don't overbuild is because it's expensive and there isn't any return. FiOS came to my building in Baltimore. I was the only person on my floor to switch away from Comcast. Even these days, people choose their broadband provider based primarily on the TV package.