The real reason is Finnish absolutely draconian fines that scale up with income and really really strict enforcement. Make fines start with $500 and go to thousands and actually enforce them and not what SF is doing and we'll have the same but people over here don't like to hear it...
The fines are not draconian. Those insane sums that end up in headlines are always from super rich folks bitching about how they should be allowed to speed because they're such net contributors.