People are already doing that in the experimental embedded world, and let me tell you, it's pain. True and utter pain. You're going to fight different versions of libusb's userland being installed, Windows/macOS/Linux kernel occupying the device with a default driver (cough rtl_sdr) and a whole lot of other messes.

Or some things aren't even available made using libusb. Think control applications for RGB lights in keyboard and mice. There's a certain manufacturer all but mandating installation of its slopware. Being able to provide all of this as WebUSB has advantages.