There is an elegant way to solve this. Mandate that whoever install the fiber lets other companies run their ISP on top of it (with a small but reasonable cut of the profit presumably). I believe this happens (mandated or not) already for mobile phone networks in the form of MVNOs.
And here in Sweden we have the same for fiber. I don't think it is mandated here, since not every place has multiple options like that, but many do. If you have municipality owned fiber (stadsnät) it always work like that I believe, often you have a choice between 15 or so different ISPs.
why would we do that? not everything has to skim profits to a certain group of people just because they exist. they can use magical competition and build it if they want a piece.
if an area has been waiting for… (what would it be now? around 30 years since the internet took off?) so these companies had 3 decades to build out and have refused, if we the tax payers step in and we pay for it, why should we let them in? they have refused to do anything for literal decades… even worse, many of these companies took billions in subsidies and still did nothing. they’ve refused to be good boot strappin capitalists, for decades.
(i want to reiterate what i said above, i believe competition can often work really really well. but if we dont understand by now that it fails sometimes too, we're not seeing clearly.)
think about how long that is, like some people become grandparents at around 35. someone born in the windows 95 days might have a grandkid and the poor sap still wont be able to get fiber. even in tons of urban and suburban areas.
some of these same ceos have gone on about how perfect the marketplace is, how awful taxes are, how magical the marketplace is… decades later if we have to build it, why should they get a piece?