I think so too.
Bevor I started to learn HTML/CSS I didn’t care how an app codes something, I just wanted it to do what it should. Thats what we expect from software and computers - to not bother us with the way it does its job.
But for example, if you tell a web design app to center a thing, it can do it using a few different CSS-methods and they all have their shortcomings or a side effect. Like using relative positioning and then changing the div that this element is relative to. This breaks it right? Or if you use a js plugin that needs „display:block“ to work, but doesn’t if you use „display:flex“. I’m sure you know much better examples than I do.
How should a webdesign software know which css technique it should use to do what I want it to do? How shall it write the appropriate css if it doesn’t know what the user is going to do or change next? It could ask the user, but then the user must have the skills to decide. This might be ok for experienced users, but it would frustrate others. Especially those users who such a web design software would target.
As long as the front end code is like it is, you probably either have a buggy beauty like Macaw, very pro-like and complex tools or somewhat restricted apps.
I think Bootstrap had an effect for HTML like what Norm says about a simpler front end language, only that it didn’t invent a new code but gave such a big variety of pre-formatted modules which just made life so much easier for those who use it, that it felt like a new frontend language.
And as for CSS it may be that Flexbox, CSS-Grid and SASS are innovations that show a bit of the potential of a simpler front end code for layout. Less error prone, more flexible and focussed on layout. Once there would be a decent browser support for CSS-Grid and even still Flexbox - I don’t know if things like that could make a Sketch/ PS/ Illustrator-like web design app possible.
But then there is something like SASS, which seemed to have produced a certain pressure on the CSS Working Group - or who ever it is - to come up with something like CSS Custom Properties. Again a web design software would have to decide which one to use.
Maybe one should throw away all HTML/CSS and come up with something new that a browser can read and parse.