Not everyone is willing to call the police, and in some areas of some cities, most people are highly reluctant to call the police. Some common reasons include:
- Anyone who would hear the gunfire has reason to avoid the police because of their own current or recent criminal activity
- Anyone in earshot knows who is involved in the shooting and knows if they try to get Marcellus Wallace's men arrested they will be hurt or killed in retribution
- The police in the area may have a reputation for being corrupt, meaning it could be useless at best and dangerous at worst to ever call them (a real life example would be the Rampart scandal of late 1990s LAPD - the basis for the movie Training Day)
- The police might be very reluctant to come to the area in question, meaning it might be useless to call them
Some of the attitudes towards the police that cause trouble in some areas are reflected in the popular culture, as in songs like "F___ The Police" and "911 Is A Joke In Your Town" (911 is the emergency services number in North America). More recently, the movie Get Out and the Black Lives Matter movement are examples of mistrust of law enforcement.
If I understand correctly, silencers are not convenient to use. They may affect the accuracy of the weapon and make get hot. Plus you have to buy and carry one to have it available when it's time to murder. So it may not make sense if you have no compelling need to use one.
It could also be a sign of machismo to not use one. What if Vincent started putting one on his gun? Maybe Jules would tease him for it.