My background is not in psychology, but I suspect is boils down to something like "I've made my decision, don't wish to admit I am wrong, and will therefore vociferously defend my position against all comers, as well as attack those who disagree with me."
1. I have an iPhone because it consistently received phonecalls when my 6N and Google Fi did not. 2. I had issues with SMS going where the fuck ever in Android that isn't an issue in iPhone. 3. iMessage's walled garden is slightly preferential because it's where the bulk of my contacts are.
Therefore I'm an Apple fanboy and apologist. I guess.
There's a similar rabid population with gaming (consoles vs. PCMR) that goes away when you have enough funding to just buy both. A lot of rabid fanboyism exists where funds are sparse.
The acknowledgement and discussion of this phenomenon is also one of the biggest reasons underlying the surging popularity of Jordan Peterson (Jonathan Haidt, etc). Human psychology is such that people like to self-segregate into teams, despite what they may say when they are being surveyed on the matter.