DUIs can be a lot more serious than just a few hundred dollar fine. They can result in the loss of your license (and consequently your ability to work), possibly several months in jail, and bar you for life from some countries (Canada won't let you visit if you've gotten a DUI.)

Spending many thousands of dollars on lawyer fees to get yourself out of a DUI can make a lot of sense unless you're in a jurisdiction that doesn't take DUI seriously. Of course it makes a lot more sense to only drive when bone dry sober.