I guess flutter web is the "hook" because it promises a "true" cross platform stack, even though imo it is still very lacking. On the other hand, QT on mobile (iOS, android) is also a bit weird, and comes with lots of restrictions and gotchas. And it basically does not have any support for web apps (except for some super recent, very experimental wasm platform support, that would probably be even worse than the "app on canvas" experience that flutter web offers)