Pro Tools was cross-platform since 1997 with the release of the PCI version of Avid's AudioMedia III card and Digi 888 interface. By then most other extant DAW

Pro Tools was cross-platform since 1997 with the release of the PCI version of Avid's AudioMedia III card and Digi 888 interface. By then most other extant DAW software, such as CuBase, had dropped Windows support, while MOTU Digital Performer was Mac-only until about 2015, though I can think of one Windows option that appeared around 1997, Sonic Foundry's Acid, which was Windows-only and reasonably popular. Regardless, the point here is that there was a choice of OS platform with Pro Tools since 1997, and yet the vast majority of established studios used Macs. The brief window that Windows had to infiltrate that space was between 1997 and Mac OS 8 when Apple's flagship OS was already desperate for modernization, and 2005 and Mac OS X 10.4, when the OS was finally both stable and performed decently. I suspect there were newer small (home) studios at the time that were fully PC, but these engineers would never consider running Macintosh. That's who used Windows... die hard PC users that subsequently got into audio engineering. But any established studios, even if they had no actual computers tracking and mixing audio until 2001 almost always went with the Pro Tools interface options running the software on Mac OS 9. Precious few studio installations that already had Mac switched to PC. New studios either invested in PC hardware initially as their first DAWs, or they didn't, but I expect most of these failed as a business for no other reason than most new businesses fail, it had nothing to do with their computer platform. So Windows started to appear in pro audio between 1997-2005, but the PC platform just didn't have enough time to ever remotely become dominant. Maybe there were a lot of Windows DAWs out there, they just weren't surrounded by a purpose-built studio generating any revenue to speak of, and among actual ground-up purpose-built studios, Windows installations were a very rare exception. That said, engineers are gear junkes, and even in Mac studios there were bound to be an old PC and a handful of cheap PC laptops for stereo on-location tracking because they became cheaper and more reliable than a portable digital recorder.