The actual driver for an HID USB device, even on WIndows, is still just a few KB.

Worse, the default driver for HID devices like mice, keyboards, joysticks, gamepads and so on is part of Windows since Windows 7 and all you had to do was give it an INF file that really just associated USB hardware devices that sent the PC a specific identifier (made up of a VID and a PID value) on USB protocol initialization, with that built-in driver - and that file is maybe 100 bytes. Even better, that INF file is not even needed anymore since Windows 10.

A driver for a mouse (pretty much the simplest Human Interface Device there is) that in addition to the normal mouse thing also supports setting the RGB color of some lights is stupidly simple because the needed functionality is already in the protocol.

Remember, modern digital electronics still uses really tiny processors sometimes with less than 32KB flash memory (and way less than that in RAM) only they’re microcontrollers rather than microprocessors now, hence the protocols are designed so that they can be handled by processing hardware with little memory (after all, many USB Hosts aren’t PCs but instead are things like USB HUDs which have microcontrollers not microprocessors)

I have no doubt in my mind whatsoever that almost the entirety of that 1GB is bloatware.