Well, the anti-Electron argument is that you're not necessarily doing it "three times for three times the cost." If you designed your app with the intention of being cross-platform to start with, you're writing it to have some kind of platform abstraction layer. The bulk of most applications isn't going to change.

That's undoubtedly still more expensive than doing everything Electron, sure. But it's going to produce a nicer application: lower resources, faster performance, working better with platform-specific features (e.g., macOS's Services menu). Maybe that's not worth it for all applications, but if Electron-style frameworks that lock their applications to the lowest common denominators become the norm, the overall quality of software drops.