It had issues all the time, and finding solutions required searching online, manually. Time consuming, difficult process. Very un-beginner-friendly.

From the throve of all possible distros, one stood out. Ubuntu. Very popular. Askubuntu Forums (with coffee beans denoting ranks) was the place when, 9/10 times, the answer to your problem could be found.

So when your fedora friend cried trying to get his camera and sound working, you either found the solutions already, or asked for them and got them. Usually the former.

That was the biggest advantage of Ubuntu. Big community and wealth of troubleshooting knowledge already available. And it had the opinion of a beginner friendly system. Which made the community grow and created a large market/userbase for help threads/tutorials.

Add to that, that people are creatures of habit and 'voila - you have a lot of people sticking to Ubuntu just because they never got so pissed at them that they would change their distro.