> Apple went all in on USB with the iMac in 1997 well before PCs were completely onboard.
"PCs" were using either parallel or serial ports, in addition to the PS/2 ports for mice and keyboards. None of them were proprietary or if they were, they were widely used so basically standard. USB ports were added easily as expansion cards on those PCs (TBH I don't recall if it was the case already in 1997, don't remember owning any USB peripheral back then)
My point is that PCs already had perfectly standards for cheap peripheral communication, so there was less pressure to upgrade to USB. I remember the "PC2000" slogan that aimed at having USB-only PCs by 2000, it probably took 3-4 extra years.
"PCs" were using either parallel or serial ports, in addition to the PS/2 ports for mice and keyboards. None of them were proprietary or if they were, they were widely used so basically standard. USB ports were added easily as expansion cards on those PCs (TBH I don't recall if it was the case already in 1997, don't remember owning any USB peripheral back then)