Open source might be very good for certain projects that would benefit from widespread collaboration. But sometimes the author is tempted to think of the software as "my baby!" Well i know that feeling.
I had a mind to release the Mr Beanbag source code along with a special edition, after i finish it (yeah yeah, if...) although not for free, and for personal edification only. But i do hope to release the game engine with an API so others can benefit from it (maybe with interfaces for AMOS and Blitz Basic as well as Asm).