"Dependency" was used loosely. The problem is one can't pick and choose the apps/services from different platforms. Say, you got used to some app on one platform. If you switch to another platform, you may lose this app. So there are barriers to switching (in addition to costs). To help the customers deal with this, the government needs to come up with the regulation to prevent abuse. If there is just one grocery store in a location, any other chain/businessman can open another store. You can't open another app store for iOS hence the need for regulation.