-rms
Apparently just insisting that it be called "GNU/Linux" wasn't too successful.
(Of course, its non-free "Mac OS X" disguise does fool a lot of people.)
What I'm trying to say, of course, is that there's no reason why multiple takes on the Unix kernel can't live happily next to each other in the marketplace. Also, you can't just blame Linux for stealing potential mindshare from the HURD... it was a group effort. There was also FreeBSD, as well as non-free but well-respected options like Solaris.
So, why? 'Cos Linux has the mindshare, and it got the mindshare because it has legions of activists (e.g. Slashdot) with nothing better to do than repeat the message to anyone who will listen. Linux hoovered up basically all the non-geek consciousness of free Unix, which means you show up to work and the company has already bought a squillion RHEL licenses and can't understand why all the engineers are slack-jawed with horror...
My cow-orkers and I all run OSX, FreeBSD, Debian/Ubuntu on our own kit... No-one I know uses Red Hat by choice. I'd love to deploy XServes at work, but again, it's a mindshare problem... Dells running Red Hat, yuck.
"In 1991, all that was left was the kernel, the brain within the brain of the computer, and thus the most essential component of any operating system, and the hardest part to create. Before Stallman could finish building his, an ingenious young Finnish computer scientist named Linus Torvalds—who was initially inspired by a Stallman speech at the Polytechnic University in Helsinki the year before—played off a Unix-like operating system called Minix to develop a free software system of his own. Incomplete in other respects, it had the kernel that Stallman's lacked—one that meshed so beautifully with the GNU system that it seemed destined for it. Strictly speaking, the complete operating system should have been called GNU/Linux, representing the combined contributions of Stallman and Torvalds. Stallman always insists on the term, pronouncing it "GNU slash Linux." But in the popular mind, it came to be known as only Linux. Stallman has never gotten over that."