Some reasons why noise reduction in vehicle cabins is not a standard feature, yet:
- As @Trevor Archibald states, safety is a very good reason. There is still a need to hear
some noises from outside the vehicle such as the sirens of emergency
vehicles: police, ambulance, fire fighters truck
- Hearing car horns from other drivers is still needed
- The sound of the engine lets people know if the engine is performing as
it should
- It's an added cost some people may not want to pay
- People haven't asked for it
- Most people don't object to hearing some noise, as long as it's not intrusive
- Insulating vehicle cabins against noise by using sound proofing
materials has suited most peoples needs until now
It has been introduced in a small number of cars: Auto Makers Shush Cars, but these are a bit more expensive than the average car. See also: Cars Go Quiet, Bose Noise Cancelling in Cars
However, introducing electronic noise reduction technology in cars, could reduce the weight of cars by reducing the amount of sound proofing materials used, Harman Quiets the Car
On a different angle, in the 1980s electronic noise cancelling had been used to cancel the engine noise made by heavy vehicles used in inner urban development site to reduce the amount of noise heard by nearby residents.