OpenSauce is [licensed under GPLv3](http://www.gnu.org/licenses/lgpl.html ""). The main reasoning behind this is to force the community to share derivative works.
Another major bullet is the fact that the engine extensions (eg, OpenSauce for Halo1_CE) don't allow for additional plugins. So a third party can't create their own special little modification and have it plug into the existing engine extension binary. The codebase is far too developed to mould it into something that could support such functionality.
Due to the fact that the Blam engine is a closed source system to multiple games, everyone benefits from shared research.
Sometimes, people create really cool food based on different mixtures of other's recipes. The same goes for code. With all derived works requiring source modifications to be released, we can see if there are things which we would like to see integrated into the main source tree of OpenSauce (a good example was the PostProcessing render modifications for Halo1_CE).