Their organization often insists they must use standard tools, and their idea of a good job is that the task works fine within their personal version. No automatic testing, no automated deployment, no version control, and handcrafted environments. And then they get yelled at when things break and yelled at for taking too long. And most DEs want to quit the field after a few years.
The real question is not that DE and software engineering are converging. It's why most DEs don't have the self-respect and confidence to engineer systems so that their lives don't suck.