Why do we not have cars with just gas and brake (automatic cars) in India as in the western countries?

Indian automobile market is very sensitive to prices and running costs - fuel and maintenance. The general complexity of automatic transmissions when compared to manual means that they are more expensive and that puts them at  a disadvantage in the Indian market. Added to that is the general notion that automatics do not provide as much mileage as a manual and are more expensive to maintain, and together you have something that the Indian automobile buyer would stay away from. However, with the congested roads and clogged traffic in our cities, more and more people are beginning to opt for the convenience of an automatic. Every manufacturer now has at least one automatic offering in almost every segment.

Car's which don't have gears are automatic car's. And we do have a few of them in India but it's not suitable here because of the constant change in speed of the vehicle due to traffic which in turn leads to very less mileage.

Price is the biggest reason. Here we have car makers selling variants with a difference of 15-20k by removing music systems, left hand side mirror, wheel caps and other items just to price their car lower. This market is cut throat.

Contrary to general belief, even auto transmission makes use of gears. The only difference is that gear change happens automatically based on speed.