[memsom]

> I suspect the company that created BeOS actually lost the source-code and that's potentially the real reason they don't want to share

Nope. The source code exists. You can find rather corrupted chunks of it archived on a very famous archiving site. The other posters are correct - it belongs to someone and they don't want to release it because it contains a lot of proprietary code and cleaning it up to make it releasable would neuter it in a way that makes it pointless. That and the ~24 years where nothing was done to it making is way past useful even to Haiku.