The issue of police taking money, in the beginning, wasn't the police actively taking money, it was the operators offering it voluntarily.
The speed at which gangs replaced each other was too fast, resulting in situations where protection money was paid to a gang in the morning, and by afternoon that gang was gone, with a new gang in power demanding all shops in the area pay all over again.
No one could withstand such torment, and in those times when the police could still stop evil, people could only pin their hopes on the police.
They would voluntarily give the police some benefits, like tobacco, alcohol, or cash, to have the police take better care of them.
Over time, this voluntary bribing of police gradually evolved into the police actively demanding protection fees from merchants.