Because infrastructure is a money pit. The up-front cost of building a last-mile fiber network is astounding (see also: Verizon FiOS) and carries with it a much longer payoff term than "next quarter." Most companies with a stock symbol have a board or shareholders that want very fast returns on investment.

(Please take the following without any hint of political bias.) A government, on the other hand, builds infrastructure that isn't intended to have a return to it that's valued in money. Instead, that infrastructure benefits society in other ways. Arguably, building a network that functions as a "dumb pipe" where others can provide services on top of it--akin to a road--would allow greater competition in the business of moving bits because competitors would be freed from each of them expending and needlessly duplicating the others' infrastructure costs.

Kind of a tangent, but it frustrates me to see when a company makes its decisions based on the desires of its shareholders (by legal obligations or otherwise). The way I see it, this behavior only serves to weaken a company. Sure, the shareholders get their 5¢ dividends, but it's usually at the cost of a superior product offering.

Capitalism, man…