React (or other web frameworks) have a unique advantage. They run everywhere.
Any device with a modern web browser can run a React application. Sure, Electron and the alternatives are resource hungry, but they allow developers to create true cross-platform applications.
Sure, there are other ways to create a cross-platform app, but none of those approaches allow you to tap into the massive number of web developers that exist.
I'm not super familiar with the space nowadays, but a few years ago cross-platform apps were full of compromises. Mobile apps wouldn't look native (tiny things like a being a pixel or two off) or they wouldn't support Linux. Maybe it's better with Flutter -- I've heard good things about it.
Additionally, Electron apps not only work as a standalone app, but you can often access a near identical version of the app in your browser. For example, you can either download Discord or Slack as a desktop app, or open them in your browser.
I'm not saying this comes for free; these apps are very heavy, and Flutter/React Native would probably produce more efficient apps.
Any device with a modern web browser can run a React application. Sure, Electron and the alternatives are resource hungry, but they allow developers to create true cross-platform applications.
Sure, there are other ways to create a cross-platform app, but none of those approaches allow you to tap into the massive number of web developers that exist.