

They’re not talking about natural monopolies. A natural monopoly is when there’s some barrier to entry that prevents competitors from entering the market, like a need for prohibitively expensive infrastructure.
What OP is talking about are situations like Walmart opening a store in a new location, operating it at or near a loss to drive the local competition out of business, and then jacking up prices once no competitors remain. The government isn’t forcing them to do that.
You might like the novel Singularity Sky. It’s about a planet, artificially maintained at a 19th-century tech level by its authoritarian government, which is suddenly visited by a post-scarcity civilization. Cellphones begin to rain from the sky all over the planet and whoever picks one up is given an offer: Tell us a story and we’ll give you anything you desire. One person asks for a self-replicating replicator with a fully stocked blueprint library and it ends up being extremely disruptive in many of the ways you’re imagining.