Most bicyclists around here are pretty careful and stay close in their lane when a car is approaching from the rear. Simple matter of courtesy and survival instinct. Even when they don’t have their own lane, and so long as there’s no oncoming traffic, they don’t weave around and one can pass them as you would another car. So my guess is yes, it’s probably a California thing.
Can you import some of those polite riders to CO? Not only do they not line up single file and maintain their space when there is oncoming traffic and someone coming from behind, they will go 3 abreast. And inevitably they’ve brought a female or a beginner rider along with them who can’t keep up, so they all have to slow down for her.