An Indian restaurant order arrives as several small bowls and a basket of bread rather than as composed plates. The format follows from the kitchen's method rather than from tradition alone.
Gravies are finished separately, not assembled
Each dish is completed in its own pan and poured straight into a serving vessel. There is no plating station where components are arranged, so the bowl is the natural endpoint.
This suits a kitchen where several orders for the same gravy may be running at once. The pan output goes to whichever bowls are waiting, which keeps the pass moving.
A composed plate would also require every element to finish at the same moment. Bowls let bread arrive hot from one station while the gravy holds temperature in another.
Bowls hold heat better than plates
A deep vessel has less surface area relative to volume, so it loses heat more slowly. A gravy spread thin across a wide plate cools before a table finishes eating.
Many restaurants serve in metal, which conducts quickly and then holds warmth from the gravy itself. The heavy base is doing the same job as a warmed plate elsewhere.
Bread cools faster than anything else on the table, which is why it comes in ones and twos as it is made rather than stacked at the start.
The food is designed to be shared
An Indian meal is built as several dishes eaten together, with each diner taking small amounts repeatedly. Individual plating would fix proportions that diners are meant to choose themselves.
Shared bowls also let a table cover more range for the same spend, since two dishes and rice feed several people who each want a taste of both.
Servers reinforce this by placing bowls in the center rather than in front of any one person, which is a different service pattern from a Western entree.
Rice and bread are ordered as separate lines
Because the starch is not plated under the gravy, it becomes its own menu item. Diners choose quantity and type, and the kitchen treats it as a parallel order.
This is why an American diner used to an all-in entree can be surprised by the check. The gravy price does not include the thing you eat it with.
It has an upside for the kitchen as well, since bread and rice are made in bulk on separate equipment and can be sold to any table without matching a dish.
The format shapes how portions are set
Bowl sizes are standardized across a menu so that the kitchen can portion by vessel rather than by weight. Consistency comes from the container, not from a scale.
That is also why gravy dishes look similar in quantity while the ingredients inside vary widely in cost. The bowl fixes the volume the guest sees.