Courts do not require a literal monopoly before applying rules for single firm conduct; that term is used as shorthand for a firm with significant and durable market power — that is, the long term ability to raise price or exclude competitors. That is how that term is used here: a “monopolist” is a firm with significant and durable market power.
Absolute monopolies do not exist. If there’s one asshole selling PC games out of a car boot, Steam does not have a literal absolute monopoly. And yet: not even Epic Games, a bajillion dollar company, has any meaningful impact on Steam’s superdupermajority control of the PC gaming market. Steam competitors existing does not mean they matter.
https://www.ftc.gov/advice-guidance/competition-guidance/guide-antitrust-laws/single-firm-conduct/monopolization-defined
Absolute monopolies do not exist. If there’s one asshole selling PC games out of a car boot, Steam does not have a literal absolute monopoly. And yet: not even Epic Games, a bajillion dollar company, has any meaningful impact on Steam’s superdupermajority control of the PC gaming market. Steam competitors existing does not mean they matter.