It’s the law of supply and demand, eventually prices increase as demand increase and the supply remains the same or even decreases. No one firm could, without the active (albeit perhaps covert) support of government, buy up a whole sector of the economy or the whole economy itself. As this firm’s empire rises, sellers would naturally demand more money from them, unless the government enforces price caps that benefit the firm. And as profit grows, entrepreneurs and potential competitor firms would see those huge profits and get into the market to compete with them, unless government actively restricts them or supports the monopoly firm through subsidy.
The economy works this way because the restrictions on these market activities are based on force. Sans force, anyone could enter that monopoly market*. The government itself claims a monopoly on force (such a monopoly is really the only objective measure of how “government-y” any given claimant government is). Thus, the government’s ability to intervene in the economy to any extent is dependent on force. Since monopoly profits attract competition like sharks and blood in the water, the only way a monopoly, and its monopoly profits, can be maintained for any significant period of time is through force.
* I might allow for oligarchic markets to emerge naturally, but oligarchic markets are functionally different than monopolistic markets. Consumers can still exercise consumer choice, just of a more limited selection of goods. Oligarchic firms can still either undersell or undermine their competitors (Apple’s approach to privacy, in addition to being something that they genuinely think is a competitive advantage of theirs, serves to undermine Google’s and Facebook’s data collection and advertising business). Plus, firms’ large cash holdings or high prices, even in an oligarchic system, still serve as a market signal to entrepreneurs to enter the market. I think anti-trust regulators need to be careful that they don’t restrict consumer choice in the larger oligarchic market in the name of increasing it in one portion of the market. By restricting an oligarchic firm’s chief point of differentiation relative to other oligarchic firms (even in the name of consumer choice or consumer protection), the regulators could cause there to be less overall choice in the market by blunting that firm’s key point of differentiation and competitive advantage. I believe that’s what’s happening in this discussion.