What is bribe ? – asking favor in terms of money/land/other objects etc to move/influence/change certain things or to perform some act which rightfully should have been performed without that favor.
Now when one has to perform certain act for which equivalent amount of energy or money are already being paid then one need not ask/expect any more money (energy) for the work they never performed (means the energy which they never burned).
Someone (e.g., an employee, employer or a service provider) may justify this by saying that because I am underpaid hence bribe is my means to mitigate/supplement that underpayment but in all other cases bribe is something for which you never made payment of energy and hence those extra energy indicates the bribe which someone gathered unfairly.
This extra energy has to be balanced out some day in some form. That balancing out varies but it balances itself overtime for sure.