They remind you that we are mortals, and not Gods cruising on effortlessly on a Heavenly Highway.
They force you to drive carefully. Anyone who has driven on potholed roads has better MOTOR skills (intended!).
Rollercoasters cost a lot to build, and maintain. Potholed roads, a lot less..
You can have competitions between neighbourhoods, and bragging rights for the guy who lives in those with big ones-My Pothole Biggest!
Kids can count them as a game, and it'll keep them away from their mobiles/gadegets for a limited period.
Not to forget, employment forever, recessions be damned..