It's in the name: **Universal Serial** Bus.

A variety of serial bus interfaces were used to connect low and medium-speed peripherals like modems, keyboards, mice, scanners, protection dongles, and so on.  Most manufacturers provided RS-232 or similar, but it was otherwise largely proprietary or platform-specific.

USB was to replace all of that nonsense.  Use any mouse or keyboard with any PC or workstation.  It accomplished that.  It was also 10 - 100x faster than the busses it replaced, which opened up new possibilities, beyond the original scope.  Hence USB 2.0.