Main reason is easy availability of developers. Can't swing a dead cat without hitting a web developer, whereas try finding one that even knows what LVGL is.

Tons of existing libraries and frameworks. Essentially every UI problem you're likely to have is solved already, there are Known Good ways of dealing with most problems that you'll encounter.

Consistent interface: the primary interaction element is the browser and HTML is the simplest thing there is to generate. You can write a basic webserver in an afternoon.

And so on...