You need government to build an ISP in the first place. No private company would be able to negotiate with that many land owners to build out fiber on a large scale.
And once a company does build a network, absent government regulation requiring them to let other companies use it, the existing infrastructure is an enormous barrier to entry.
Telephone lines were almost always built following existing public roads or private railroads (that were built with government assistance and government land grants) even in the early days.
There is no history of a successful, large scale infrastructure project built without government assistance. Either directly or due to the fact that much of it was built on government land.
(unless maybe you consider some case where private infrastructure was built in one large area controlled by a small group of owners, but that's basically just a government by another name and doesn't apply to modern America.)
railroads were given the go-ahead by the federal government back when they were built, because the federal government granted the land to both sides of the rails to the rail builders (if they built it).
It's hard to argue that the railroad builders were not given "assistance" (the granting of land).
And once a company does build a network, absent government regulation requiring them to let other companies use it, the existing infrastructure is an enormous barrier to entry.