I really wonder: why wrap it in Electron, instead of simply hosting the emulator as a regular webpage on one of the free hosting services?

The "hard part" of making it run in a browser engine is already done. WASM is supported across all browsers with good performance. There is absolutely no advantage of running it in Electron, and it's harder for the user to install (since Windows SmartScreen will most likely block the installation, and the macOS version is distributed as a zip file.