Many most? cities do have noise ordinance laws that would prohibit choppers, but then cops have to decide if that want to take on that battle. Most bikers are super friendly. Some of them are not. One of the biker gangs in my area use a cocktail of drugs that make them fearless, angry, violent and it usually takes half a dozen cops to take down one of the bikers.
It does, but most cops have spouses and children to go home to. Given options, they will lean towards writing tickets to people less likely to be violent. This is easy to fix and has been fixed in some cities, but then the blowback usually goes the other way. Citizens will complain that the department has been over militarized and will demand the department lose funding until all the military gear has been removed.
