In TeX the line breaking depends on the whole paragraph. I imagine it could be visually quite distracting if the line-wrapping jumped around in a WYSIWYG word processor as you added text to a paragraph.

Edit: ah. I see this is noted in the posted article’s To-do section:

Figure out how to deal with dynamic paragraphs (i.e. paragraphs being edited) as their ratios will change during editing and thus visibly move around.