An Indian restaurant menu in one American city closely resembles one two thousand miles away, down to the section headings and the order of dishes. That uniformity has specific causes.
The format arrived as a complete package
Much of the American Indian restaurant model was inherited from an existing commercial format developed elsewhere, including its dish list, its section structure and its kitchen method.
Adopting the whole package was far easier than designing a menu from scratch, particularly for operators whose expertise was in running a restaurant rather than in menu development.
Because the format came with a proven workflow, changing the menu would also have meant changing how the kitchen worked, which is a much larger undertaking.
Staff mobility spreads recipes
Cooks move between restaurants and bring their repertoire with them, so a dish prepared one way in one kitchen appears the same way in the next.
Restaurant openings frequently draw staff from established places, which transplants an entire working method rather than a single recipe.
Because the same movement happens repeatedly across a region, kitchens end up converging on a shared way of cooking that nobody deliberately standardized.
Suppliers reinforce the standard
Distributors serving Indian restaurants stock what those restaurants order, and what they stock determines what is easy to put on a menu.
An operator wanting an ingredient outside that set faces higher costs and less reliable supply, which is a real disincentive on a dish that may or may not sell.
Customer expectation is self-reinforcing
Diners who have learned the standard menu look for its familiar items, and a restaurant lacking them reads as incomplete rather than as distinctive.
That expectation makes deviation risky. A new restaurant is safer carrying the expected list and adding its own dishes alongside than replacing the list outright.
The result is a common core with a small variable section, which is exactly the structure most American Indian menus display.
The convergence is now loosening
Restaurants opening in metro areas with large South Asian populations increasingly serve narrower regional menus, because there is a customer base that does not need the standard list.
The standard format still dominates in markets where it is the only Indian restaurant for some distance, since there the menu has to serve every possible customer rather than a particular one.