There are many reasons WordPress is popular; it is easy to use and it comes with a wide variety of plugins, like wpDataTables, that offer advanced functionality with a very simple setup. Yet, there are some situations when you need to know how to edit HTML in WordPress.
However, from time to time, you have to access the source code of your website. For example, when your site gets attacked by a malware, it might crash your entire website and there is no other way to fix things except for playing around with the code a little bit.
On the other hand, there might be situations where you simply want to make some advanced customized changes and you need to know how to edit HTML in WordPress.