Basically, it's because we expect markup to have meaning. The situation is pretty different from what it was with a traditional GUI builders because of the markup hiding back there. In the bad old days, Dreamweaver had visual tools for this stuff, and it generated a horrifying mess of nested tables. This was rightly criticized because it made for a huge amount of markup, the markup was difficult to embed in a generat…
I'm not a front end developer, and don't really have any desire to become one, and I would like to have a GUI for building fairly standard UIs.