If you want to maximize code-sharing, you would use webtech for all platforms, including iOS and Android. Yet most organizations don't, because they know that that gives them a poor experience, and they're willing to expend the effort to do native ports to those platforms.
Alternatively, if I'm not making a web application, I literally don't care about the fact that I could share my desktop code with it, because it doesn't exist.
...and my point is that nothing about Electron makes it uniquely able to solve this problem. Someone who can't use my app would also appreciate GTK/Qt if it allowed them to use it.
Some people are also unable to use apps because they use Electron. My computer can't play some video games while I'm in a Discord call because of how many resources it uses, but it's perfectly fine in a Mumble call, because Mumble has a reasonably-performant, non-Electron client.
GTK is a non-starter for something professional, at least if the experiences of the GIMP and Inkscape on macOS are representative. (Also, it's C, which does avoid some ABI problems, but it's hardly suited for an object-oriented environment)
Planning to release this next week!