But I think the reason VS Code has become so popular is that along with its editor centric UI it has Emacs like extensibility. Plugins are easily written in JavaScript and it originated the Language Server Protocol which makes it possible to write language integrations in the target language.
I've not used the newer version of IntelliJ since the redesign, but I always found it somewhat overwhelming, with all this stuff which prevented me from focussing on the code I was writing. The old version had pretty poor UI performance too, whereas the VS Code UI is fast enough that I rarely notice any UI slowdown.
Nevertheless IntelliJ is pretty indispensable for Java/Kotlin development. It's code sense features are excellent and there are a lot of projects out there that don't really build except through IntelliJ's automatic Gradle setup.
FWIW the only pop-up like things I see with VS Code are extension suggestions when I open a file with a new language extension and the monthly update change logs.
In VS Code, I usually see a file explorer, the files I have open, the Problems panel and a terminal panel. All of the other stuff is hidden behind sections that, when clicked, simply replace the file explorer. Far less visual clutter
Complicated GUIs (most GUIs targeting 'advanced' users, IME) likewise cause sensory/attentional overload for me, as well. If an escape from that kind of design is part of what drives people to VSCode, I totally get it! For me, keybindings and a command palette (or similar) are a much more natural way to include lots of cuntionality in an app without making it overwhelming to navigate visually.
A few other aspects: - dark mode by default - web tech UI, not terminal - decent looking widgets and decorations
I don't think these are the main selling points for vscode, but they do all of this better than their competitors.
