You’re being pretty selective there. MANY states require an Ignition Interlock Device:

http://www.ncsl.org/research/transportation/state-ignition-i...

This not only costs thousands of dollars – a very significant amount of money to the vast majority of Americans – but it also SEVERELY limits an individual’s ability to drive a work vehicle.

Yes, prison time is not always involved, but the financial cost of a DUI can be quite serious.