This actually happened to me: I arrived at my destination and discovered my load was loose, ready to fall. There have also been times that I dropped something. And times that my backpack was mistakenly unzipped and I could have lost something worth keeping.
So if I operate with your assumption (that honking drivers are always assholes), then I lose the opportunity to pick up something I dropped or correct insecure cargo. Why should I give that up?
(edit) Since a horn is an ambiguous signal, in this circumstance of a car following a cyclist it should come to be universally understood to mean a cyclist dropped their phone or wallet, as this is the legit scenario.
Enforceability varies depending on the scenario. Some countries have law that holds employers accountable for tax evaded by workers. Employers obviously won’t gamble, so they refuse to pay cash and cryptocurrency wages because they are scared shitless of being accountable for an employee’s evasion.
I demanded cryptocurrency payment and my employer refused on that basis. I intended to continue declaring it properly and just wanted a bit of freedom from bank dependency, but nothing could overcome the employer’s fears.