Well that's not strictly true.

OSS is allowed to make money and there are projects that require paid licenses for commerical use.

The source is available and collaborative.

Qt states this on their site: Simply put, this is how it works: In return for the value you receive from using Qt to create your application, you are expected to give back by contributing to Qt or buying Qt.

There is nothing in the open source licensees that prevents charging money, in fact, non-commercial clauses are seen as incompatible with the Debian Free Software Guidelines.

And there is a lot of companies out there that make their money based on open source software, red hat is maybe the biggest and most well known.