I use Atom because it looks great, is crazy flexible, and it's lightweight in terms of features. It's an editor first and can be turned into an IDE progressively. I love the idea of IDEs. I just get overwhelmed with all the tabs and buttons everywhere because I really only need 5% of them.
Atom is not an IDE and it shouldn't be compared to one. It's more akin to Sublime/Notepad++/vim. It's a text editor that you can bend to your will (e.g. https://junolab.org).
The biggest downside to Atom in my opinion is its performance. Historically, it's been pretty sub-par and over the last 2 years it's improved. Atom >=1.30 is a different story and today atom is just as performant for me as VS Code and I do use both and develop extensions for both of them.