Whats Wrong in Car Pooling?

I dont understand why people in Mumbai dont use Car pools. I have observed that almost every car plying on the roads is carrying just person (the driver/owner) or two persons. Meaning for every 100 cars travelling on the road, maximum number of people in them might be just over 150.

However if people use car pool, the number of cars on the road carrying the same number of people would go down to 40. That is 60 cars (or at least 50 cars) less per hundred cars at the moment. This should help to reduce the congestion on the roads and the pollution in the air by half.

I know this makes sense. But still people dont use car pool. Why?