I am actually focusing on learning WordPress right now. From a glance, it does look like just a build your own website style, but that is not fully true. WordPress is very powerful and is a great skill to have - especially if you want to be a freelancer.
In a nutshell, WordPress is a CMS. In other words, it manages my images, videos, blog posts, comments, users, etc. so I don’t have to constantly update HTML files, tweak databases, and all that annoying, time-consuming stuff.
This is a misconception. WordPress manages your code not replaces it. I still develop the front-end for my site. I am in charge of how the website looks and operates. I have just added WordPress to make it easier for me or my client to update the page himself.
Wordpress plugins let you supercharge your development. Do you want to have a contact form that sends emails? There is a plugin for that - you don’t have to build it. Do you want to have an image slider? Automatic backups? There are plugins for almost anything on WordPress that help you and the client out tremendously. As a developer, you can also develop custom WordPress plugins for people.
True, there are people who use WordPress as a website builder - they aren’t your clientele anyway. WordPress is useful because it makes it easier for you as a developer with plugins, and it makes it easier for your clients to manage their own website without having to contact you all the time.