Selfish ownership who won't allow staff to be gifted by customer

I'm a frequent shopper at Spar in Ormonde, visiting up to 5 times week. The staff are always very pleasant. On Sunday 14th December I was in line behind a staff member and offer to pay for his meal. The manager walked up to us and told me I'm not allowed to. Staff are not allowed to accept gifts or any kind from shoppers which I find totally appalling. The manager was not very diplomatic in his response and you clearly see the other shoppers were not impressed. Why can't we offer a little gesture to show kindness and gratitude. This store needs to right itself and it's attitude towards their staff.