Most of the train station vendors in the UK sell two types of food. Long life sandwiches from companies with a sale or return approach. And frozen products that are heated up. They don't have the staff or space to make products on site and are dependent on delivery. So it is really a logistics problem. The quality is usually better at stations with enough volume for more regular deliveries. My hunch is that less "developed" countries in Europe source local fresh products rather than rely on a logistics system. But in the UK the local producer probably won't be able to compete on price and does not want to bother with a relatively small volume of sales. And local companies find it hard to secure concessions in train stations so can't sell the product themselves.