There all sorts of laws, reforms to those laws, and then there are those unwritten laws. It has been said that America doesn't have any legal ticket quotas or arrests quotas, but the reality of the situation is that police departments most definitely have both ticket and arrest quotas, though they aren't designated as such. For instance, traffic tickets and citations bring in revenue, which is designated to the State, county, city, and locality, in which the budgets that have been created are based upon anticipated revenues from those tickets and citations. Further, when it comes to arrests, the whole infrastructure of jails, lawyers, probation/parole offices, and courts are dependent upon having an ample supply of arrestees to process, fine, incarcerate, and also to utilize for no-labor cost community service. In addition, some communities have signed contracts with private prison facilities, which mandates a certain occupancy rate of inmates, in which any shortage to that percentage, the State or county responsible for that contract, are held accountable and therefore must pay the private prison facility a penalty for having not provided enough prisoners or arrestees.
Additionally, police officers in the field have an obligation to fill out at a minimum a contact list, of what that particular officer has been doing and accomplishing on a given shift. So that, an officer that consistently produces little or no arrests is going to have an issue with their responsible supervisor, because a very common metric in the efficiency of any officer is the arrests accomplished on a given shift, and to come up short again and again, represents a red flag. This signifies that officers that do not meet their explicit or implicit arrest quota, are going to be made well aware of it, because they are now cognizant of the truism that an officer that is not making arrests is not doing their job. Therefore, once an officer becomes aware of what is expected of them, they are almost for a certainty going to produce the arrest numbers so needed.
So then, when it comes to arrests, police officers, aren't necessarily going to want to go to the trouble of finding real crime and real trouble, but instead have a strong tendency to want to spend their time arresting the types of people that have little money, few assets, no connections, and meager resources to fight the criminal justice system. The very purpose of doing this, is because if police officers spent their resources on arresting those in white-collar industries, and harassing citizens that live and work in very nice neighborhoods and spend their money at very nice venues, then those people, collectively, would not put up with such targeted harassment, and would thereupon do everything in their power to stop such; because the purpose of the police for those people is to protect and to serve them, not to harass, intimidate, and to arrest them, for they collectively have political, legislative, and by implication, judicial power, and will most definitely utilize such, by all means, necessary.
Instead, the police recognize that the easiest people to arrest are those that have no power, and therefore make for easy targets, thereby pleasing their police superiors as well as keeping well oiled the machine of arrest, judicial processing, incarceration, and post-incarceration monitoring, all combining together to produce the filling of that machine with product, and poor people are the inventory that need to be utilized on a continual basis for that machine, and therefore quota must be met, and the poor and powerless are that abundant resource to be mined again and again for that very purpose.