AppStore is not a speadsheet or a word processor. It is not a graphics editor or text editor. It is a package manager. That is the kind of software it is. AppStore "automates the process of installing, upgrading, configuring, and removing computer programs for a computer's operating system in a consistent manner." That is its type. That it sells things does not change the fact that it is a package manager.

Many are hedging words, confusing a market, where you might purchase bananas and soda, with an economic market, AppStore is strictly not an economic market, i.e. not distinctly "a composition of systems, institutions, procedures, social relations or infrastructures whereby parties engage in exchange." AppStore is in an economic market, the market of package managers for handheld devices.

You can't force MacPorts to accept your software. The maintainers and regents of MacPorts are pretty reasonable, but if you develop software that locates children for sexual abuse, you're probably not going to be allowed to distribute your software with MacPorts.

In kind, if you violate the terms of Apple's developer agreement, which you must agree to before you can even download their developer tools, Apple has the absolute right to ban you from distributing software in Apple's (it belongs to no one else) AppStore. It is not anti-trust behavior. It is written policy.