Actually, a lot is: Google "cable franchise agreements" or "city broadband franchise agreements" and you'll find that many if not most cities and counties either forbid or make prohibitively expensive real competition. Here is one news article about a lawsuit related to them: http://stopthecap.com/2012/06/19/court-invalidates-existing-... .
Many states are also passing telco-financed laws prohibiting local municipalities from creating Internet access as a utility. Examples: http://www.infoworld.com/d/the-industry-standard/big-carrier... or http://www.slate.com/blogs/moneybox/2013/12/30/municipal_bro... .