In Switzerland we basically had ISP monopolies back in the day on cable (DOCSIS) and on the phone (xDSL) networks. Prices were ok, but not low. Then fiber optic as a viable tech came around, but neither of the large ISP was particularly eager to build out a fiber infrastructure, as it was more lucrative to just sit on their “old” tech, knowing the ohter party won’t be building fiber, so won’t have a better offer either
So what happend then was that munincipalities built their own fiber networks, renting them out to the ISPs, large and small ones, either as an IP service or as dark fiber for ISPs which want to provide their own equipent. Only the largest ISP still builds their own fiber infrastructure, in parallel, and they are required by law to rent out that infrastructure to other ISPs as well.
This has really leveled the playing field, brought good competition and lowered the prices.
So I think government owned infrastructure is the way to go, but it takes a long time to build out and needs the right policies and legal framework to succeed.