* Red Hat Linux (previously the go-to desktop linux) was discontinued in favour of RHEL/Fedora in ~2003.
* Ubuntu was first released in 2004.
* Around 2000 a new release would come as a CD image and the normal way of upgrading was to wipe out everything except your home directory. This meant trying out a new distro was pretty much as easy as upgrading your existing one.
* As you say, although Yum was released in 2002, apt-get had been around since 1998, and so at that time was more mature.
* Wifi became increasingly common, and almost always needed proprietary binary blobs. Proprietary ATI and nvidia linux drivers became available. And of course MP3 was widespread.
Ubuntu arrived at an opportune moment - former Red Hat users looking for a new home, users used to wiping their system and installing a new distro, and clear benefits if wifi, graphics and MP3 all work out the box.