Apple stops you from going to Android? That's new to me. Apple owns the platform, so they own what rules happen on the platform. They are not the only platform. Don't like how things work within the platform, including the Appstore, go to the majority holder, Android.
Are you being intentionally obtuse? The retail metaphor doesn’t hold because stores don’t act as gatekeepers to customers once they shop at a store (there is generally free movement for any person at any given point in time).
The whole point is that once a company reaches a certain size and market share their behaviors (if anti-competitive) can lead to deteriorating market conditions which is bad economically.
Most people/governments around the world have agreed that it is best to prevent these behaviors so that competition can continue to drive innovation/creation.