Why don't we stress on these points:
-It provides the opportunity for young developers to discover new and advanced techniques that may be hidden in proprietary software thus improves their knowledge and they are able to start where others ended
-It encourages collaboration and contribution spirit and lets people work together instead of the usual individualitic approach
-It increases the rate of development drastically due to the afformentioned group work
-And of courses it gives a wider chance for freelance developers to compete among each other and creates a lot of freelance job opportunities at low cost for the outsourcer instead of having to invest thousands or even millions in proprietary development tools and training, taking into consideration that this investment leaks out of the national economy
-This added value to individuals' knowledge is an overall added value to the national economy as the added value does not always consist of money but of know-how as well
That's what I could think of so far..