I don't know why it died, WYSIWYG and GUI-friendly IDE's allowed higher productivity in that "one-man-bands" (small staff) could do the entire project. Now development is often layered into specialists. Things like UI design and ORM's have longer learning curves, which emphasizes specialists. But staff is larger per feature: less productive. (There are many times I wanted to shoot Bootstrap in the head when I couldn't get it to act how I wanted. Something in WYSIWYG that would take 20 seconds becomes a 2 day trial-and-error session in Bootstrap.)
WYSIWYG/GUI-IDE saved money. Most businesses don't run their internal productivity software on mobile anyhow. "Progressive" UI's are a money sink in practice.
The trend predictors got it WRONG: desktops live on in biz. Our anti-state-GUI web standards don't help. Businesses really want cheap rich desktop-like GUI's for productivity software.
I'm not against flow-based layouts, but they should be an option, along with WYSIWYG.