Without an app platform there would exist no software.
>I have a macbook and barely use the apple store.
The app platform is more than just the store. If you can install an app without the apple store, that app has to be able to run and actually do stuff somehow. The way it is able to run is the app platform.
>If they prevent me from running any software apart from through their platform
If you do not want to run software using Apple's hardware and Apple's software then Apple is effectively out of the picture. Apple won't prevent you from running apps on a different app platform like Android.