Why? Ubuntu is based on Debian and I guessing it shares and contributes to same package ecosystem.
> Debian (upon which Ubuntu is based) has been around for decades
Found Debian, after being around for decades, never quite won the desktop market. Debian got there perhaps 80% ofthe way, but the final 20% was just hard to achieve, and I think Ubuntu put a great effort into that 20%, polishing it up and making it a much better experience. After trying Debian, CentOS, Mandriva, Gentoo for my dev machine, I ended up with Ubuntu, and with it I stopped worrying about my OS. Almost everything works. I don't even think about or notice the OS anymore. And that's a good thing!
So, back to Debian, once I want to deploy something and I've played with it on my Ubuntu dev machine, which OS would I evaluate first? Ubuntu Server, of course. So I think the server story paradoxically often starts on the Desktop.