[JohnStrange]

Do you have any numbers to support your premise? "Few" is relative and in the eye of the beholder, and I personally don't have the impression that only few projects 'monetize'. There are a lot of commercial open source projects, I find out about a new one almost every day. However, you may be right if what you want to say is that only a small percentage of the total number of open source projects monetize. The same probably holds for proprietary software, too, most of it is in-house or developed by hobbyists and only few proprietary software projects successfully 'monetize'. And let's also not forget that the vast majority of all projects, be they open source or not, are probably abandoned/given up.

[AstralStorm]

The most interesting one from the failed business perspective is Blender, commercial project turned open-source via a bounty.