With a city's roads already built, there's no place to safely put the cyclists. The difference in speed between bikes and cars requires the bike lanes to be separated by more than a painted line. In many US cities, they make the shoulder into a bike lane which is just a bandaid, there's not enough room to put in a real lane protected from vehicles.
I never trust the painted in lanes, as people on their cell phones or distracted occasionally drift into that lane. Drivers aren't becoming more cautious, just the opposite.