Because Ubuntu included proprietary drivers by default, notably ATi and NVIDIA and Wi-Fi cards, all of them were so tedious to install on Debian (which was one of the most popular Linux distributions at the time)
It also shipped latest free software from two months ago (GNOME, X) that actually worked on a 6 months schedule! (Remember Debian releases back in the day? If you attempted to get your USB flash drives to just work, you'd otherwise be recompiling half of your system and Gnome with Garnome or jhbuild)
And it shipped actual, physical CDs across the world for free. It was 2004!
Then it shipped a free LTS that may not have been as stable as RHEL, but it was definitely fresher and with guaranteed updates (for main) for 5 years (3 on desktops early on). It was 2006.
