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.
A WordPress website is made up of themes and plugins. Themes control the way the page looks, this is where you as a front-end developer become important. You develop the way the page looks just like you normally would (HTML, CSS, JavaScript). But WordPress provides a dashboard allowing you to easily manage the website. You can edit your paragraphs, images, and everything from a control panel like you would in Microsoft Word. This is great if you are making a website for a client. You make the WordPress theme, and now they can tweak it however they want. Information, photos, prices change over time. You no longer have to change it for them - they can do so themselves.
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.