Let's see if you shed a tear when a car breaks and city hall (this is, all the citizens, including you) has to pay for it.
It's typically done in "problems areas" where a small number of people drive 25-50% or more over the limit, but it's extremely frustrating, because it forces drivers to drive way below the actual limit when crossing the speed bumps - especially if they're the bolt-down kind. i.e. the effect is to cause irritation for ~99% of drivers in order to punish a tiny minority.
[1] I'm sure it happens elsewhere in the US, too.