Happened to me one year. No pins because 'they are not allowed' !. All very odd. A moment's thought would show the vendor could not be liable for anyone hurting themselves, or anyone else, with the pin unless, perhaps, the sale was to a child so young that it shouldn't be trusted with a pin. Other vendors offered pins at the time, so it must have been a private, not the charity's, decision
It's not really a matter of health and safety.
Is this a true story or an urban myth?
Maybe they are afraid of litigation but I bet they sell sharp knives (to adults) so it seems silly not to offer pins.