Earlier quoted context omitted.
Why should the government be doing it?
There's no reason the government actually needs to build the infrastructure itself—but since infrastructure is a natural monopoly (only room for one set of roads, one EM spectrum, etc) the government needs to "regulate it into existence", setting laws to incentivize cooperative building of neutrally-owned infrastructure by interested players, rather than the natural monopoly leading to a real monopoly/oligopoly.
Of course you realize that there's debate about whether government makes this scenario more or less likely.