In the mid to late 1990s, USB was scarce. It didn't take off until after Apple replaced its ADB (Apple Desktop Bus) port with USB in the first iMacs. Once that happened, manufacturers flooded the market with consumer products (e.g. CDRW drives) and PC makers followed suit. Up to that point PC makers had standardized on the serial port.
I don't have contemporaneous links at the moment but the second paragraph of a relatively recent (2015) article summarizes:
> But Apple shocked the computing world when it swept its old connectors away with the original 1998 iMac. The bulbous computer adopted a then-struggling standard developed by Intel called USB (Universal Serial Bus). In a hint of what was to become the company’s ability to make or break certain technologies, USB would go on to live up to its “universal” descriptor and become the most prevalent connectivity standard in the world. The solid-and-hollow stacked rectangles of its “A” connector now appear in everything from alarm clocks to airplanes. [0]
[0] https://www.fastcompany.com/3044088/apple-and-usb-a-history-...