From Section IV of the Justice Departments article: The Supreme Court has noted the crucial role that defining the relevant market plays in section 2 monopoliz

From Section IV of the Justice Departments article: The Supreme Court has noted the crucial role that defining the relevant market plays in section 2 monopolization and attempt cases. The market-definition requirement brings discipline and structure to the monopoly-power inquiry, thereby reducing the risks and costs of error. The relevant product market in a section 2 case, as elsewhere in antitrust, "is composed of products that have reasonable interchangeability for the purposes for which they are produced--price, use and qualities considered." Thus, the market is defined with regard to demand substitution, which focuses on buyers' views of which products are acceptable substitutes or alternatives. For search advertising, they will likely find other forms of advertising such as Facebook as a good enough substitute and thus the market definition will include other forms of advertising and not just search. For app publishing, you can publish your app for android yourself which Fortnite did. iOS distribution on the other hand can probably be argued for that and in fact they are getting sued for their "abusive monopoly in iOS app/in-app distribution services" [0]. [0] (PDF): https://www.hbsslaw.com/uploads/case_downloads/apple-dev/2019-06-04-complaint-apple-developers.pdf https://www.hbsslaw.com/uploads/case_downloads/apple-dev/201...