https://www.techdirt.com/articles/20180423/08363539691/doj-investigating-att-verizon-making-it-harder-to-switch-wireless-carriers.shtml

AT&T and Verizon have enjoyed a stranglehold over fixed and mobile residential broadband for years. They also enjoy a relative monopoly over broadband business data services, a market that services everything from cellular tower backhaul to ATMs. Given that both companies have a rich, deep history of engaging in all manner of dubious behavior to keep these markets as uncompetitive as possible, there would be absolutely no shortage of ammunition for regulators seeking to punish them on antitrust grounds.

Given that both companies are politically powerful campaign contributors, that generally doesn't happen, regardless of the party in power.