Some people like the looks. Some people buy one because it serves as a status symbol. Some people just go with the flow and buy one, simply because everyone else already has one. Some people appreciate the coherent UI. Some people already use various other Apple products and services, so they prefer to get the synergy of also using an iPhone.
I don’t really care much about any of those things, but I have some special software and hardware that only works with vanilla or OEM Android and iOS. Trust me, I tried lots of different tweaks and hacks, but eventually had to face the harsh reality that nowadays things are specifically designed to prevent people like me from doing whatever I want. If things had worked with Lineage or Graphene, I would obviously be using those instead. Since that isn’t the case, I had to pick the least offensive one from a list of two awful options. This decisions shows that I value the compatibility that comes with an iPhone.