ISPs are NOT a natural monopoly, you can have multiple sets of wires going to every building. This is the situation in my part of Europe and my internet is pretty damn fast.
Treating ISPs as a monopoly is fundamentally wrong.
Multiple sets of wires going to every building is feasible and perhaps even reasonable when we're talking about an apartment building. But digging multiple trenches along suburban and rural roads and driveways leading to single-family homes is very wasteful. It's usually prohibitively expensive for the second company that wants to come into town, and is basically guaranteed to be a negative ROI for the third company that tries to lay fiber to customers who already have two incumbent options.
In the US, Google Fiber has had limited success entering a handful of carefully-picked markets where the incumbent options are rotting copper POTS wires vs coax that can only compete on downstream bandwidth. In some of those markets, the incumbent phone companies have replaced some of their copper with fiber, but a third residential fiber option is still unheard-of. That may not fit the strictest definition of natural monopoly, but it's pretty close: in areas where both Google Fiber and eg. AT&T fiber are competing against coax, it would not be surprising to see one of the two fiber ISPs give up. We've already seen Google give up on bundling TV service, and both Google and AT&T are very reserved about further expansions.
Also in Europe the owner of a cable to a build is required to rent it out to other providers at cost. So if DTAG builds a cable to my apartment complex, then I can later go an buy a DSL from Vodafone, despite the line begin DTAG. Since it's at cost, Vodafone has no further costs than what they would pay if they put down the line themselves, they even save some since they typically delegate support to DTAG technicians for on-site issues.
Yeah, the US had a similar concept that was changed about 15 years ago for phone circuits. Owner of the "dry pair" had to lease it out at a regulated rate, around $10 a month. At the time that was still law/policy, I had great DSL service through an independent ISP. It was far more reliable than the other options available at the time. The legal change destroyed that entire company, and left me with the typical duopoly choice for broadband since.
Treating ISPs as a monopoly is fundamentally wrong.