Because the leftists with a brain have enough space in there to recall that it doesn't work that way in practice and just becomes another avenue for the .gov to screw a few more bucks out of whoever can't fight back.

Traffic laws if enforced uniformly would be massively unpopular and get changed. You might be able to get people to bend over and take it like they do in Europe but you'd have to boil the frog for a couple hundred years to get to a state where that's culturally acceptable in the US. Traffic laws enforced discretionarily just become an expensive wheeled version of stop and frisk but with a pretext that makes them constitutional which is not good for society. The status quo of having traffic laws be mostly unenforced except in the case of egregious violations and with occasional spot enforcement is closer to optimal than the jackboot fantasy. Of course there are places where improvement can be made but such opportunity is mostly incremental.