Restaurants with a handwritten menu of six dishes that changes weekly are usually assumed to be making a statement about seasonality. The practice is driven mainly by purchasing and kitchen capacity.
Buying at market prices requires flexibility
A kitchen committed to a fixed menu must buy specific ingredients regardless of what they cost that week, which transfers all price risk onto the restaurant.
A kitchen that writes its menu after buying can take whatever is abundant and therefore cheap, and can decline whatever has become expensive.
Over a year that difference in purchasing is substantial, and for a small restaurant operating on thin margins it is frequently the difference between viability and closure.
Short menus reduce waste to near nothing
Every additional dish on a menu requires its own ingredients held in stock, and anything not ordered enough that week is either used elsewhere or thrown away.
A six-dish menu drawing on overlapping ingredients allows almost everything bought to be used, and allows quantities to be estimated accurately.
Waste is a direct cost with no offsetting revenue, so reducing it improves margin more reliably than raising prices does.
Small kitchens have hard capacity limits
A kitchen with three people and limited surfaces can only execute a certain number of distinct preparations well within a service.
A long menu forces more items to be prepared in advance and held, which shifts the cooking away from the moment of service and flattens quality.
Restricting the menu concentrates the same labour on fewer dishes, which is the mechanism behind the consistency such places are known for.
Suppliers reward the arrangement
A grower with a short glut needs a buyer quickly, and the restaurant willing to take the whole quantity is the one that gets the best price and first refusal.
Those relationships build over seasons, and a kitchen known for taking what is offered ends up with access that a fixed-menu restaurant cannot obtain.
This is why the menu often reads as a list of ingredients rather than dishes, since the ingredient is the decision and the dish follows from it.
What it means for a diner
Reading a menu published online is unreliable for these restaurants, since the version served may be entirely different by the time of the booking.
Dietary requirements are best raised at the time of booking rather than on arrival, because a small kitchen buying to order can accommodate them only with notice.
Asking what the kitchen is pleased with that week tends to produce a better meal than choosing by category, since the answer reflects what was actually bought well.