It does not work because the old IBM clone mouse does not speak the USB protocol.
There are at least three kinds of mice:
- Mice who only speak PS2.
- Mice who only speak the USB protocol.
- Mice which understand both, detect which pins are connected and 'speak' the right language.
A passive PS/2 to USB plug only works on the last set.
An old IBM clone mouse sounds like type 1.
If you want to use that you will need an additional device which understands both the PS/2 protocol and the USB protocol and which translates between these two.