I think collars are nowadays similar to rings on fingers. To some it means the world, others just like how they look or feel, and then there is perfunctory aspects, too: Collars and chokers hide anatomical features the wearer might be uncomfortable with. They also help for not constantly losing your headphones.
Stopped making assumptions about why someone wears a collar, sometimes there are clues hinting to a backstory but as I find it with many aspects of one's appearance: If you want to know, you have to ask. And that is a beautiful thing in my book.