Not a product manager but I habitually try to play devil's advocate as one. I think it's popularity, full stop. You _could_ vibe code a native app no problem - but then you're targeting one set of hardware. If you're already just vibing it, why not make something that will work cross-platform while you're at it? And if an LLM is prompted with that, they'll usually go with the popular choice: web app on Electron.

There are plenty of cross platform options. I write with Qt for example.