Even a few years ago when CMS webdesign started designing websites became very easy but a lot of people still held on to what the knew and a nowadays famous cms system like joomla was new and many people thought bad about it, calling it cheap because of the Open Source. When webdesigners used cms, then they prefered their own cms which they could call special. Because of it being a privat system they could charged their clients a few hundred bucks a year for using their cms.
Allthough Drupal was going for a time neck to neck with Joomla, it's certainly loosing ground now, mainly because their back-end is that as understandable as Joomla's. Ok it might be the best, but it is too hard to operate for the everage person. Wordpress is doing fine,specially for the bloggers it is a good and easy to handle system. But lately I am most impressed by the Joomla webdesign and templatebuilders for Joomla like Rockettheme are amazing. Their Gantry back-end is given a webdesigner and even their clients such timesaving options to modify the whole template's css, it is hard to believe they will go on improving this sytem. Ok, it is maybe not that easy at first sight but if you use it for a while it all comes clear.