McVoy on BitKeeper, Linus, and Perens
Joe Barr writes "The story of how BitKeeper has come to be Linus Torvalds' (and many other kernel hackers) tool of choice in maintaining the Linux development tree is worthy of a book. Here's the Cliff Note's version of McVoy's contribution to Linux kernel development, BitKeeper, and countless hours of flaming on the role of open source and proprietary software."
BitKeeper, otoh, sells software. If they Open Sourced it, they'd loose a lot (most) of the sales of their ownly product.
Different companies, different products, different focus.