Well, I know that in 1998, I was a die-hard Microsoft advocate. NT was a real Server OS, and the only reason anyone used 30-year-old Unix anymore was because they didn't have a chance to upgrade yet. I understood NT, could support any type of NT problem, and was going to get my MCSE.
But now what am I doing? I'm working on AIX and SCO OpenServer, and wouldn't touch MS products if I didn't have too. What caused me to change platforms? Was I tired of waiting for NT 5? No, as I learned even more about what kind of OS NT was, I realize what a poor implementation it was, and how much superior of an implementation that Unix-type OS's had.
Also, I saw that the MCSE wasn't very valuable, and people were getting it who had no understanding of NT at all. Why would I want to get an MCSE having an understanding of advanced NT concepts, and then be associated by doofuses? Also, why get stuck working with an OS that has no "escape" route. When I learned Linux, I had a skill that I could adapt to many other platforms. But if I focused on NT, then I would have been stuck with NT jobs. I would be at the will and whim of Microsoft. But with Unix, I can go from Linux to FreeBSD to AIX to Unixware, without needed massive amounts of retraining. I am no longer locked into one vendor.