I guess letting your cup sit in them while you are not actively drinking so that it keeps your cup upright and doesn't fall over. I suppose it beats standing your coffee cup on the flat portion of the console and having it spill in the seat, floor, or worse, in your lap. I don't think you would call that a fascination with cup holders, but only common sense, since we as humans drink liquids, and liquids tend to me a mess if spilled in nice cars such as a Tesla. How do you keep your cup upright?
Oh, and I don't think that is a "fascination" - just another comfort creature in an automobile - comes in very handy at times. I don't think I'm going to spend a whole lot of time worrying about it - but cup holders ARE worth a comment on a message forum. I don't day dream about them or anything (if that's what you meant by fascination).
What's your fascination with other people's fascinations? (since I made one post about cup holders and you called it a fascination, I can only assume that your one post about fascinations means you have a fascination with other people's fascinations)