So the key difference of size is the ability to find alternatives. If a monopoly is abusive, you rarely have any options. If a smaller player makes an abusive p

So the key difference of size is the ability to find alternatives. If a monopoly is abusive, you rarely have any options. If a smaller player makes an abusive play, consumers will abandon it and it will fail. Google and Apple are a duopoly but since they've both decided on the same abusive practices, consumers have no exit without government intervention. Basically, antitrust works in a world that expects the market to correct things, but patches a design flaw (monopolization) which prevents the market from doing so.