It usually a combination of stubbornness and insecurity. I work in a mixed environment and have a friend group that varies in usage, so there is a group that likes to "joke" about it. For the record, all the tech savvy people at work are Mac people except for 1 guy who is PC/Android. I am know to use a lot of Apple stuff.
I never tell anyone how great Apple stuff is or brag etc. However, I do get a lot of questions about "how to do stuff" on the computer...which is a Mac or PC.
I have totally forgotten how to use a PC more or less. So what usually ends up happening is I get an email or phone call, with a long story about how someone is frustrated they can't edit a PDF/sign a PDF/presentation is wrong/videos don't work/something doesn't sync etc etc. I then send them a 1-4 step answer for Mac, which is either a free or cheap solution, or involves buying an apple device that does EXACTLY what they want reliably (wireless backup)
They then get mad because "they don't have a mac" or "that program cost money" (keep in mind this is for something that is usually kind of important). So they spend about 3 weeks trying to figure it out, get a fix from the PC guy, it breaks, they can't do it reliably etc etc. You would think after a while the aggravation would be not worth.
So I honestly think they just take it out on the mac user. I mean, I get jokes about how my gear is expensive. Sure, it cost more. But guess who's calendar, email and documents are always up to date and synced? Who edits and signs PDFs professionally in a matter of minute? Who's presentations work and are formatted correctly on the projector? And the video come with my presentations too. And so on and so forth.
That all being said, there are Apple users who also don't know how to use their computers. But they usually get their stuff figured out much faster and the solutions last longer.
I guess some people are just penny wise and pound foolish.