Comment by userbinator

Some still have two, for a keyboard and mouse:

https://static.tweaktown.com/content/1/0/10071_10_asus-rog-m...

Latency is lower because it's interrupt-based and much simpler than the polled USB stack. IMHO if you're going to always have a keyboard and mouse connected to the computer, it makes perfect sense to keep them on the dedicated simpler interface instead of the general USB; especially when the dedicated interface will be more reliable. The industry may be partly moving away from the "legacy-free USB everything" trend that started in the 2000s, finally.

AFAIK all SuperIOs support a pair of PS/2 ports, so from a BoM perspective it's not an extra cost to the manufacturer, but they still market it as a premium feature.