I don't know if/don't think that Qt's licensing is an issue for most of the people who need to make cross-platform applications and reach out for Electron. Electron seems to be the default choice not just for FOSS projects, but also for commercial projects, which have no qualms using a toolkit that might go proprietary, and can get a commercial license if they need it (which most of them don't).

GTK, on the other hand, yeah, it hasn't been a good choice for cross-platform development for years now. The only platform it properly supports is Gnome.