The problem with sustainable monopolies in a free market is that there are a hundred thousand ways to skin a cat. Even if a particular business has a lock down on a particular resource it can't control alternatives. The only way a monopoly can be sustained is that businesses price things so low that there isn't any profit in competing against them with alternatives. And that is not really terrible and is not likely sustainable anyways.
Most people seem to operate under the misconception that somehow large corporate interests and large governments are opposing and balancing powers.
This is untrue.
Large businesses and large government are interdependent and complimentary. They feed into each other. They need each other. If you want bigger business you need to have bigger government.
The sort of ultra concentration of capital in the hands of a tiny minority of businesses and individuals wouldn't be possible without the government creating a regulatory environment to ensure that it happens first.