There are differing levels of enforcement in different places, but I've made thousands, possibly tens of thousands of infractions on my bike in 35 years of commuting, sometimes right in front of the police, and I've never had a ticket. Is a rule really a rule if it isn't enforced?
If I say everyone needs to wear clown shoes to work on Wednesdays, is that a rule? It doesn't mean jack-shit because I can't enforce it.
Drivers are held more carefully to the rules of the road, but given that they're ensconced in a protective metal shell, they have a lot more leeway with the law of the jungle. With cyclists it's the other way around.