[mcv]

It is explicitly why Standard Oil was broken up. Look up pretty much any anti-trust case. It's very common, and the reason it's not even more common, is because it's explicitly illegal by anti-trust law.

> When the prices are low that sounds like a good outcome for their customers.

No, because it's only temporary. They only lower the price to drive the competitor out of business, and once they're out of business, they raise the prices again.

> there isn't anything preventing another newcomer from emerging

Yes there is: investment. If every newcomer goes out of business like that, that makes it a bad investment to enter that market. You are already at a disadvantage entering a new market because of the investment needed. If you then can't recoup those costs, there's not much point in even trying. And the established big players can and will drop their prices to run you out of business unless stopped by regulation. Your argument only works if you ignore investment costs necessary to enter a market.

There's literally more than a century of legal history behind this.