I can't claim any authority on this topic, because I only witnessed the tail end of it as a clueless junior dev, but one thing I saw at a couple of companies was Linux creating a less risky path to commodity workstation hardware. People with Unix-based computing workflows saw that they could achieve something similar on Linux on commodity hardware, and the hardware was cheap so it was wasn't a huge risk to try it out. After they were successfully working with Linux and could see that the commodity hardware was sufficient for their workflow, then it wasn't so radical to cast their eye over to Windows and see what software was available there, maybe be tempted by more polished desktop software and easier IT solutions for businesses. And they could try it out by dual-booting their existing Linux workstations. I'm sure some people made the double jump straight from commercial Unix workstations to Windows, but for people who did not want to take any big risks, Linux broke up the leap into smaller steps.
I think a large factor was that many engineers had a PC on their desk as well for MS Office, email, various corporate apps made in VB (before the web), and so forth.
When x86 & NT became good enough for whatever engineering application they were working with, there was a large incentive to switch that one to NT and consolidate everything on one machine.
