And even if it were a full blown cross compatible mouse driver with a lot of device features it is hard to fathom why such a driver would require more than a megabyte or a couple of megabytes of space. The basic functionality can be realized in less than 30k.
We had the whole operating system with GUI (Win3, OS/2 and Linux)run in 4 Megabytes. Sure it was snappier with 8 Mb, but that is still a far cry from the minimum requirements the commercial OS offerings come today.
The way we are wasting ressources is simply insane
You probably don't use an ancient OS as a daily driver so maybe those extra megabytes really are needed for something important after-all. I'm not saying Windows is super well optimized for space but you can't count the whole growth as waste. Even the default Raspbian Linux for Raspberry Pi requires several GB of storage.