I think the reason behind using React and JavaScript is simpler - these tools are heavily vibecoded, and React/JavaScript is what was most present in the training data and as such is what the models excels the most at generating.
The crappy laggy UIs have the same root cause - heavy use of vibecoding with lackluster quality processes
The crappy laggy UIs have the same root cause - heavy use of vibecoding with lackluster quality processes