"Bright vest law would be easy for cops to ticket AND get the careless bikers off the roads."

Only some of them. There are plenty of careless bikers who wear helmets, have lights, and wear reflective clothing. There are also plenty of responsible safe bikers who are helmetless, obey all the traffic laws, and wear dark clothing. Sometimes their invisibility makes them more careful, because they are aware they can't be seen easily.

A bright vest law won't change irresponsible behavior, and it only gets careless cyclists off the road if it's enforced. Since careless bikers don't generally kill people in a crash (other than possibly themselves), and the police are already stretched thin, any such law would have a low enforcement priority. It may make a larger number of cyclists more visible to cars, but as we've seen in 2 recent bike-car/truck crashes, a cyclist can be riding within the law with all the proper safety and visibility equipment and still get hit by inattentive drivers. (Sparling was likely in the truck's blind spot, so I'm not counting that fatality - it was due to substandard / inadequate safety equipment, not an inattentive driver)