It may also have to do with perhaps a "lemming" mentality.
If you get into shooting because of a friend/acquaintance whose opinion you respect, you might tend to adopt their opinion(s). They use X brand equipment - it works well and so you too get into that brand, while shunning the others without ever trying them.
I learned in high school with Pentax, so when it came time to buy my own, that's the brand I looked for at the store (yeah, no internet back then)...in the used section, of course. No Pentax, and all they had was an AE-1 w/a 50 1.4. An excellent camera, the sales guy said, and it turned out he was right. I used that for over 10 years, happily.
Then in the 90's I wanted to treat myself to autofocus, so back to the store (not the same one, still no internet) I went. I was looking for Canon, but alas my FD lens wasn't compatible, and so, long story short, I went home with a Nikon (I kept my Canon though) because of the whole "they didn't change their lens mount like Canon did" thing, and that sounded like a good system to me.
Well, having used both, I can say I prefer Nikon. I don't think the gear is any better or worse, but I'm heavily invested in that system now and have no interest in changing.