I think I addressed both ways around: markets naturally tend to settle on 3-5 competitors, unless blocked by regulations.
There are very few markets that are both natural monopolies and stay that way for long periods of time. Outside of things that tend to be owned by governments anyway, like road networks, I'm having a hard time thinking of any.
You're right, I apologise for not reading your post carefully enough.
Whilst pure monopolies are rare, my impression is that surprisingly many markets consolidate to an oligopoly, and that this reduces competition and is generally pretty bad for the consumer.
There are very few markets that are both natural monopolies and stay that way for long periods of time. Outside of things that tend to be owned by governments anyway, like road networks, I'm having a hard time thinking of any.