PS: Sorry I think I was wrong, had an edit open but failed to submit: I believe that I was thinking of keyboards that did the same (in particular of Cherry key

PS: Sorry I think I was wrong, had an edit open but failed to submit: I believe that I was thinking of keyboards that did the same (in particular of Cherry keyboards), not Logi mice. The same, and for longer I think, because PS/2 held out so much longer in its keyboard variant. At first because of unreliable (or missing?) USB implementation on BIOS level, then because of lingering distrust. Where PS/2 continued to exist surprisingly long (perhaps still?): the internal connection from laptop mainboard to touchpad. Not the DIN connector, but the protocol. And as a consequence, the cheapest external touchpads (those riding the efficiency of scale of the much higher volume internal market) had been PS/2 for a surprisingly long time.