France's situation: national public telecom company (France Telecom, now Orange) built the network, private competitors appeared, Orange got privatized, competi

France's situation: national public telecom company (France Telecom, now Orange) built the network, private competitors appeared, Orange got privatized, competitors didn't have the network to be everywhere and allow proper competition so the law forced Orange to allow other ISPs to use Orange's network for a fee (so I could be a client of, say, Bouygue Telecom, but using Orange network to join Bouygue's). A huge and easy justification for that is that Orange's network had mostly been built using public funds since it was a public company at the time. Since then, several competitors have built their own network, but most still use Orange's sharing for remote place, small villages etc where it's not worth it for them to deploy their own. So your question is hard to answer. Why has the monopoly ISP built the infrastructure ? Because it was a public company, and if you wanted your house to be connected to the network they had to do it. Why have the others built their own ? Because it was much cheaper for them long term, especially since they also use it for their cellphone network. And from what I see, it seems to be the same in a lot of Europe, the national companies made the original network, and competitors piggy backed on it until they had their own. (I've oversimplified of course, but that's the gist of it)