To be fair to that there wasn't really any other viable mass-market interface that the keyboard manufacturers in China/Taiwan could standardize on. The PS/2 keyboard interface was backwards compatible with an AT keyboard through the user of a passive physical pin adapter. And USB didn't exist yet.
Oddly enough, the SGI Fuel (also the Tezro, I think) had PS/2 keyboard and mouse ports but also offered USB ports and support for HID devices in IRIX.
I have no idea whether the keyboard and mouse that shipped with those later SGIs were PS/2 or USB devices.
edit: IMO there was nothing wrong with preferring PS/2 to USB 20-some years ago. Higher theoretical refresh rate on the PS/2 mouse at that time and the PS/2 keyboard offered better n-key rollover, although I question whether any of that mattered one way or the other to an SGI owner
In x86 i386 world there was a good long overlap of ATX/MicroATX motherboards shipping with both PS/2 keyboard/mouse ports and also USB ports on them, starting from 1998 era Pentium 2/3 systems when USB first became commonplace and continuing until probably 2010 or so.
I am currently at a customer site installing a brand new mainstream budget computer purchased off the shelf from a brick and mortar retailer (Microcenter PowerSpec B687) which has PS/2 ports and a VGA output right next to the USB/HDMI/DP paired up with a 14th gen i5.