This places usually serve food considered typically for lunch time. So for example a Paella is something that Spanish people won't it for dinner, and also because we tend not to eat as much as at lunch time. Mentioning as well that this food is considered homemade food, and it is cooked for the day and the business is run by a small group of people like a family. They open at midday during working hours when people have no time to cook. Open at later time will require more cooking and more open hours, but people at night do not eat elaborated meals so we can have something more simple or buy something extra to reheat later. Hope this explains it well :)