You think people who tear up the street to put in sewers have never thought "hey, while we are at it, let's build some conduit down here and then sell that?"

I know they literally work on sewers, but they aren't dumb. They understand their business better than random people on the Internet do.

My brother used to do utility plumbing — literally, laying sewers. I know they think this. It's not them that's the issue; it's short-sighted municipal governments, it's contracts, it's "Well, who's paying for it?", it's liability issues, it's these and countless other little inanities.

That said, it kinda blows my mind that someone on HN would actually think I was talking about the people laying the sewer line when I said, "Well, while we're here..." Were you straw-manning, or did you really just not think that one through?

So please tell us, why is it not done? Contract provisions? Lack of profit?

Both.

Most common, SewerCo says "pay for half of our digging costs" and FibreCo says "You're getting paid by the city to dig it up already! Why should we pay again?"and round and round we go. Also, if either SewerCo or FibreCo's work has delays, then there's another whole drama about who pays/is responsible for additional work, penalties, and so on. And the respective Project Managers don't give a rat's ass about the other company since hitting their budget/timeline is the only thing that matters.

Seems like something that can (and should) be worked out, but unless local government steps in and mediates/forces their hand there doesn't seem to be a great urgency. Locally (in NZ) ElectricCo and FibreCo are starting to be the same company in a number of cases, in which case "stop arguing and just do it" is just a management edict.

This is why the municipalities--in the United States--that have city-operated utilities should be doing this. In Seattle, for example, Seattle City Light is the legal owner or half-owner (with the local telco) of every utility pole in the city, along with ground easements for electrical service. Since Seattle City Light and Seattle Public Utilities (the water and sewer provider) are two departments of the same city, they share the same easements and access rights. Tearing up a street to rebuild the street, reconstruct a sewer, or bury electrical wires is all done by the same entity, so adding in fiber conduits is easy as long as there is the budget.

Sadly, that last sentence is the kicker. "As long as there is the budget." There's no line-item in the city budget for building a municipal data network that covers the last mile (Seattle has a rather sizable not-quite-last-mile fiber network).