- I used it for email, then I had to collaborate with people who wrote "please see my comments in orange below". (Of course, they were Outlook users.) Emacs did not show that orange color, so I didn't know... Maybe these days it's possible to read Outlook emails nicely in Emacs.
- I used it for development, then the Java software I worked on got too big to internalize all APIs and Eclipse completion and refactoring really helped. I did try to build the Eclipse "quickfix" thing in Emacs, but all I got done was to add a missing import (because JDEE, I think it was, provided that functionality).
- I switched from Linux to Windows because the world around me was like that, and so I could help junior colleagues with their EOL problems...
- I used Mercurial (hg) for a while and TortoiseHg was really nice, so I didn't feel the need to use Emacs for this.
It's a pity, really. Some aspect here, some aspect there, and then you get pulled away from Emacs.
Now, with LSP, perhaps Emacs could offer code completion and refactoring, but the Java app I work on builds with gradle, and I have no clue how to tell the Java/LSP thing about the class path... So I'm on IntelliJ...