Ubuntu came to be in a time when RPM-based distros suffered badly from dependency hell. Ubuntu was built on a very reputable and stable Debian base and made it

Ubuntu came to be in a time when RPM-based distros suffered badly from dependency hell. Ubuntu was built on a very reputable and stable Debian base and made it more desktop-friendly by installing certain drivers by default. For a while Ubuntu was the most likely distribution to have everything or most things work out of the box on many systems. On top of that, yes, marketing.