There's plenty of cross-platform UI kits for a wide range of languages.
The thing that's big about Electron is it allows web developers to use their existing skills to create desktop apps.
A lot of web developers would like to make desktop apps, but aren't willing to learn a new systems language to do that, especially when there's a solution that lets them use the JS + HTML + CSS they already know.
> The thing that's big about Electron is it allows web developers to use their existing skills to create desktop apps.
Also it lets you reuse parts of your web app (or build part of your web app while building your desktop app). For something like Slack, or if Google were to make a desktop version of Docs, it makes a lot of sense to use Electron because you already have your web app and you want your desktop app to be consistent with it.
I've used Ionic with a very small team to make a web app and mobile app from the same codebase. The client asked if we could also make a desktop version for them, and instead of taking months to build one and make it consistent with the web/mobile apps, it was just a few days of learning to wrap it up with Electron. That was really neat!
For me, JS+HTML+CSS isn't (I had to outsource most of the UI code to our webdevs), but Qt or GTK (or, god forbid, Cocoa and whatever is Microsoft's newest fetish) are so much less productive that I just cannot justify writing in it any more. If you want a smooth UX with things like animated scene transitions (people scoff at animations, but if used sparingly and at the right places, they improve usability), or just any non-standard widgets, it's far, far easier to do everything in HTML.
And the beauty of Electron is that you can still write all your actual logic in C/C++ and use Node's FFI to bind it to your UI.
(Qt is transitioning to the same model with its HTML+JS based Qt Quick orchestrated from native code; but it's far less production ready than Electron right now.)
The type of developer that only knows one language of any kind is in the same boat. Electron is popular because folks can write products at a faster pace than they could in other toolkits and languages. Being unproductive and fighting your tooling is not a sign of competency, nor is it a rite of passage. If folks can write apps faster in Java or Rust (which I love writing, by the way), I'm sure Electron would not have the adoption curve it does. Nothing to do with only knowing one language.
I also know Python, Go and Rust, but I only use them for tinkering and experiments. I'd still use JS+CSS+HTML via Electron for a GUI app over traditional systems languages any day of the week.
The thing that's big about Electron is it allows web developers to use their existing skills to create desktop apps.
A lot of web developers would like to make desktop apps, but aren't willing to learn a new systems language to do that, especially when there's a solution that lets them use the JS + HTML + CSS they already know.