Debian's weakness, if you can call it that, is their rigid adherence to being totally open source.
Generally that's a good thing but when I need to play an MP3 I don't want to have to jump through a bunch of hoops to do it.
That's where Ubuntu and Mint and some of the other derivatives came in. They took the stability of Debian as a base and put desktop functionality into it.
And in Ubuntu's case added support for proprietary, yet ubiquitous, server-side hardware.