I was recently teaching a class in working as a voter registrar. I noticed that I had brought a box of pens and mentioned that the students I was training would need to have a box of ball points with them when they were registering voters.
We treat pens as free goods. While banks still have delicate chains on their pens, nearly everywhere else pens are treated as trivial. Restaurants lose a lot of pens to people who are signing credit card receipts.
Part of the reason is because ballpoint pens are very cheap. But we are not so generous with other cheap items like water and air at gas stations (in Calif. they require $.50 in coins) or ice in bags, or soap in public bathrooms.
We are generous with cheap items when they are part of complete transaction such as a coffee shop where we give napkins, sugar, cream and paper cups. Or gas stations where we give paper towels, window cleaning fluid and sometimes coffee.
It could be pens are treated as free because they are cheap AND they are not usually part of another transaction that is being bought.