When you take money in any form of contract you're required to follow the rules of said contract.
The US government entered into a number of contracts with Facebook thereby requiring Facebook to conform to said contract(s)
The lobbying is set up to avoid legal issues with those contracts they already signed.
You have copies or can point to these contracts? I’d like to see this contract if one exists between Facebook and the US government. Especially one where Facebook somehow surrenders its Constitutional rights.