The money is always ads.
What Electron does is project presence. It's not huge, but also not insignificant.
If Mozilla controlled "the thing developers use to make desktop webapps", they would have more presence. I also think their solution was nicer, and developers would have loved it.
Firefox was a thing for developers for a while. And that made it healthy.
How do you suggest Electron makes money for OpenJS?
You can still make PWAs backed by Firefox:
https://github.com/linuxmint/webapp-manager
This has not made Linux Mint any richer.