That's the genius behind parse (from the perspective of their creators): they don't have to run your code, so they don't even have to think about all the issues that come with that (security, CPU usage, etcetera). Firebase used the same trick.
It's genius to get started quickly, but quickly becomes an architectural nightmare. If you need to change a query and the logic is in the mobile app then its going to be days before Apple approves a new build, and even longer before the user updates to the latest version. If your logic is on the server side then you roll out the new code and you're done.