When I discovered Joomla a few years ago, I thought it was the crown jewel of all open-source Content Management Systems. I couldn't wait to learn it's inner workings, and show everyone else how awesome it was. At the time I ignored WordPress completely. After all, all it did was blogging. I wanted something that would allow me to manage a website, blog, store, and whatever else I could imagine. Diversity was my main goal, and Joomla provided that for me.
So why did I switch?
Joomla - It's been a few years, and other than the introduction of a few new features introduced with Joomla 1.6, It has remained the same CMS. It hasn't included any groundbreaking features that users are looking for. URLs are still the same pain they used to be. The back-end is still just as confusing to end-users at it used to be. In the past, Joomla's best quality was in it's simplicity when creating a custom template. One page was all it took to create a design. Nowadays, that one file looks messy and unreadable to anyone but me.
WordPress - On the other hand, WordPress has done nothing but improve it's feature set. With each new update, we've seen things like custom post types, better menu systems, user interface updates, better theme support, and much more. They've taken a blogging platform and made it extensible to the point where entire websites can be built around a fully customizable administrator area. Add to that the fact that the WordPress administrator interface is clean, simple, and easy to use for the average Joe, and there is already plenty of reason to make the switch.
WordPress and Joomla are both powerful content management systems, and they both have their place in the web world, but the improvements WordPress has made far outweigh the mediocre progress of Joomla.