WARNING!, I am about to start ranting:
(rant)
There was a time when I was always using an IDE: Turbo C++, Visual C++, Visual Studio, IntelliJ, Eclipse (horrible). They were good tools, and I made good apps and got paid to do it. Then there were challenges in which I was forced to think outside of the IDE, and one of the challenges was build automation. I would need a server that checks out code, runs the compiler, runs the tests, and uploads the build. Even though I was editing the build script inside an IDE, it didn't serve its full purpose, it was merely there as a text editor. Not to mention I had to FTP the script back to the server. I thought of using an FTP plugin on my IDE. Nevertheless, it was still very incovenient. I wasn't proficient at ssh and scp, or vim. The whole process was arduous. It sucked, and I thought this was what being a sys admin was like.
Then I started learning vim, then tmux, then starting to understand the GNU toolchain, sed, awk, grep, piping output, and all the nix stuff. Then I started to understand why people do this.
An IDE is like the swiss-army knife, but bulkier. Imagine owning a 10-in-1 tool, and you sit there wielding the tool, but all you need is the screwdriver. IDE is great for that all-in-one development environment, but it's just that, a development environment. Sometimes you don't need the entire set of tools, you just need one.