Technically you could use the same application (as in, same UI and features) across the three major OSs.
(Although you could make the same argument for something written, say, in Java)
The notion that "you could use the same application across the three major OSs" is the feature – the feature is not that it uses Electron. That it uses Electron to accomplish the feature is incidental.
It scales
But the new benchmarks say MySql is faster, why should I use that instead of this image viewer ?
Scale what? Humans can still only look at a couple of images at a time... (or was that a joke?)