Earlier quoted context omitted.
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.
So please tell us, why is it not done? Contract provisions? Lack of profit?
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.