FYI the United States had line-sharing requirements for DSL service until 2005; that could always be reinstated if the FCC actually wanted to rely on a competitive market for ISP service.
Actually, there are certain technical characteristics of DSL that make it better than cable (DOCSIS) for certain use-cases. Fiber obviously takes the cake, but fiber has not been rolled out everywhere yet.
DSL can barely compete anymore.
The only reason that it can is that there is no competition.