Google Play Store is filled by badly described applications, malicious programs and projects incorrectly classified in terms of the age of the potential customer. That's why Google updated its app developer policy and firm started cleaning up their Play Store - when Google will finish its plan, then big number of apps will be removed permanently from Play Store.
How we can read on official Google's website, firm won't allow for publishing apps which "appeal to children but contain adult themes". Applications which will have content about hate against specific races are now especially banned too. Google will try also to solve problem with apps which work at the similar way as other programs from Play Store to make the database of programs more varied. In Play Store after update of Google's policy we won't find apps responsible for cryptocurrency mining like MinerGate.