Joomla is indeed always a good option but I would say that its peak popularity was a couple of years ago. Right now it has fallen behind WordPress and that can be due to several reasons. The WP development has been going on great and many new features were introduced for that time.
But I think the main separation point between WP and Joomla/Drupal would be the learning curve. Joomla and Drupal may still be the top choices for developers, but for the common man, the Average Joe, user-friendliness is what matters most. Everything is moving very fast and many people don't find the time to sit down and learn something new. They want something super easy, self-explanatory and yet capable of functioning as they want it. This is where WordPress excels and why it has such a large portion of the market share imho.