IIRC, all the previous distributions have been obsoleted once Ubuntu was available.

I mean,yes and no? At the time, Ubuntu made itself an extremely prolific and easy to start linux experience. The adaptations that ubuntu presented have been replicated in several other distros now, and Canonical have made questionable choices to the point where Mint seems like THE beginner/minimal config distro, the things that are universally acceptable from Ubuntu are being rolled back into debian, and mint itself is trying to go for a debian based version which is basically the same level of friendliness.