Naïve question I'm genuinely asking my self: why? What is the reason it is so difficult to implement WYSIWYG not top of HTML/CSS (i kind of feal it thinking at

Naïve question I'm genuinely asking my self: why? What is the reason it is so difficult to implement WYSIWYG not top of HTML/CSS (i kind of feal it thinking at latex,but can't put a reason other than "organisation of the source")? on top of which kind of serialisable representation would it be easier, is there any..?