Dishes that are firmly breakfast food in southern India show up on American menus at lunch and dinner. The relocation is driven by restaurant economics and American meal habits rather than by any change in the dishes.
Breakfast trading is a hard business in the US
A restaurant opening early for breakfast pays a full complement of staff for a period when the check average is low and the customer count is unpredictable outside of established chains.
Independent Indian restaurants generally cannot support that. Opening at midday and running through the evening concentrates labor and rent into the hours when people are willing to spend more per head.
The dishes therefore move to the hours the restaurant is open. Nothing about a dosa requires morning, so the constraint is entirely on the business side.
American diners do not classify them as breakfast
Breakfast in the United States is a narrow and strongly defended category built around eggs, cereal, pastry and cured pork. A fermented rice crepe with potato filling does not map onto it.
With no breakfast slot available in the diner's mental model, the dish is filed as savory food, which means lunch or dinner. Menus simply follow where customers expect to find it.
Portion and pricing follow the reclassification
Sold as a main course, a dish that would be a light morning plate at home has to justify a dinner price. Sizes grow, fillings become richer, and accompaniments multiply.
That is why an American restaurant dosa is often far larger than its counterpart in India and arrives with several chutneys and a bowl of sambar as a complete meal rather than a snack.
Menus also proliferate variants, since a category holding one item is hard to price against. A page of numbered dosa variations makes the item read as a main-course section.
Prep time argues for the same shift
Fermented batter needs to be ground and left to rise, which cannot begin at dawn on the day of service. Batter made yesterday is ready when the kitchen opens, whenever that is.
Because the fermentation window is fixed by the batter rather than the clock, the kitchen has an incentive to sell across a long service rather than a short morning one.
Weekend brunch is the partial exception
Some Indian restaurants in larger US cities run weekend morning service, which is where these dishes recover their original meal slot. Weekend demand supports the labor that weekday breakfast does not.
Diaspora customers drive most of that trade, since they arrive with the original classification intact. The same plate reads as breakfast to one table and as brunch novelty to the next.