For whatever reasons the combination of regulation and competition in the UK has worked to provide effective competition and meaningful accountability. Despite the default network being owned by the former monopoly, regulation has achieved meaningful competitive access (other telecom providers can located their machinery at telephone exchanges for example). And it keeps it separate from the funds of the government, who will otherwise find the temptation to cheese pare irresistible.
Your comparison with roads is interesting. Privatising the freeway network would ensure that payments made for road use actually get to maintain the network. Historically the 19th C turnpikes were indeed maintained in the UK on that basis, but were later nationalised. I suspect that given the state of the potholes in many countries, a private body charged with road maintenance receiving specific payments from users could be a very useful way forward.