At the very least, releasing their source would make available any bug fixes or enhancements they've made so that other users can choose to incorporate or learn

At the very least, releasing their source would make available any bug fixes or enhancements they've made so that other users can choose to incorporate or learn from those changes. Yes, this is a case of tivoization in that you can't load modified bins onto your car, but arguably you don't want people to be doing that to their cars anyways.