How about a _market_ is anything where there exists a _marketplace_? Doesn't seem like a wild stretch. Now why should Apple have a monopoly on accepting payments on its platform?

To your second point: people are sad that we can’t have cheaper and better software on iOS. It’s a poor UX when an app makes me go on my desktop to sign up for their paid service. It negatively impacts consumers and only exists because Apple is wielding its monopoly.