You still need hardware significantly more complex than would be otherwise needed for a device for which USB 2.0 speeds were already much more than required.
I don’t really understand how USB stuff works (what is the difference between a hub, interface, and controller?) but from what I’ve seen I think a hub supporting 20gbps would probably be in the 5-15$ range and probably not larger than a few centimeters
What is really unnecessary is to have the ability to transfer 20GB/s from your mouse or keyboard.
If you have multiple ports driven off the same internal hub, they will share bandwidth.
You still need hardware significantly more complex than would be otherwise needed for a device for which USB 2.0 speeds were already much more than required.
I don’t really understand how USB stuff works (what is the difference between a hub, interface, and controller?) but from what I’ve seen I think a hub supporting 20gbps would probably be in the 5-15$ range and probably not larger than a few centimeters
That is true. Lets go back to PS/2.