It's the same reason you see barbers working well into their 70s.
After a lifetime offering a service to your neighbourhood, cutting hair and having a chat, why would you even retire? Just to stare at a wall, useless and lonely?
There was a barber down the street from my former work place, and I had no idea what his hours were. He seemed to just show up and work when he felt like it. Clearly was semi-retired.
Was a great story teller and joke teller. That was worth the price of a haircut by itself.
But serving your community coffee every day seems like a great way to stay involved in your community doing something useful.