Part of it stems from the fact that wholesalers, in addition to raw ingredients, also sell partially prepared pre-packaged meals to restaurants. A number of restaurants resort to this model, in particular major chains (Applebee's, IHop, Waffle House, etc.) as it means less kitchen staff to hire. This is at least very common in North America, where Sysco is the goliath and has cornered the market on this front. Perhaps the same thing is happening in Spain?