The situation where somebody is being forced to pay a bribe is already illegal. Why do I actually have to pay it in order for the authorities to do something a

The situation where somebody is being forced to pay a bribe is already illegal. Why do I actually have to pay it in order for the authorities to do something about it? This seems erroneously predicated on the assumption that the briber is doing so because he knows the payer will be complicit in the crime. I think the more likely scenario is that the briber does this because he has no fear of the authorities or their ability to enforce such laws.