There are a few different reasons that Google has made it their policy to not allow 4shared users to upload their own apps. The most popular is that Google does not want people creating multiple versions of the same app or duplicating the code. Another reason is that 4shared was already doing what the search engines do - share files between websites. The new change by Google makes it harder to share files within the same app. This is especially true for those who share files between an iPhone, a Windows phone and an Android phone.
4shared is one of the first big apps to be affected by this change. If you're an iPhone user looking to download an app, now might be a good time to look for a different service that supports the iPhone. If you're an Android phone user looking to download an app, it's probably not a good time to use 4shared just yet. There will probably be other apps that will continue to work with the new 4shared format.