That's not entirely true. You can have a free ISP market, for example, where the last mile infrastructure is owned by a government-sanctioned monopoly which is required to lease to any ISP which applies. The infrastructure might be a (government-owned) monopoly, but a free market operates on top of it, providing much better competition and services for the customer than if the last mile was not a monopoly. That's how it's done in the UK where BT owns the phone infrastructure, but is required by law to lease it to ISPs, including leasing it to BT's own ISP at the same rates. That gives a shit-tonne of competition, as anyone can tap in to that market and become an ISP without having to dig trenches or wire up entire cities on their own.