I've been asked this question over and over again, expecially since Wordpress gained popularity and became widespread.

The first part of the answer is simple: habit. When you start working in one system and when you realize it's advantages, you simply continue working in it and you become better and better which results in satisfaction. The second reason is that Joomla! offers everything an administrator/designer needs: complexity, vastness of (free) extensions, developed administration, good support and stability. You can do a lot of things in Joomla! automatically: you simply download and install an extension you need and the system is ready to work. But if this way of solving things doesn't satify your needs, Joomla! is flexible enough to allow you direct access to the code: ie., programming. Joomla! supports the latest technologies besides php, so you can also program in javascript, jQuery, CSS3, Less, ajax, but also supports technologies such as Bootstrap.

Many web solutions are developed for Joomla! to simplify work. I personally rely on  Gantry Framework. Among number of good framework systems, for website design and creation I place this excelent framework in the first place. It lacks a detailed user interface design system, but extended posibilities of coding make up for this imperfection. We shouldn't neglect other frameworks: T3, Expose, Vertex, Yougrids, Warp which I tested and presented in one of the articles (5 most popular theme frameworks for Joomla).

When talking about websites, I didn't limit myself only on website creation, but also on SEO, (I was employed as an SEO specialist for two and a half years). In 2014. I cooperated in the startup project called StepUpIT and lectured at the College of Slavonski Brod on web programming (html, css, php, jquery, Joomla, Web shop, SEO).

In the future I will focus more on developing my JavaScript and UX skills and implementing them with Joomla!