Originally Posted by potter

It's just how it works. When you pay for an app to be developed, you're paying for the end-result / finished product. The source code is owned by the person who wrote it. Unless there is a line item in the contract specifically outlining it. Source code is by default (legally) copyrighted and owned by its writer, and the writer has to explicitly hand over that copyright to someone else.

So, if you want the source code - you need to have that stated in the contract agreement. If you're already past that time - you'll need to see if they'll accept payment for the source code.