I think a passive agressive "fuck you" is an important element because it provides enjoyment and some satisfaction to the corporate drones who you are interacting with.

I think allowing low level minions with saddistic tendencies to express that saddism via a kthxbye-but-actually-fu here and there is used to reward them for an otherwise boring and unfulfilling task. In this case it is a bit indirect because it is the developer who wrote the code not necessarily a clerk at the counter or a customer service representative in a call center.

Don't remember the incident, I think it was when someone was fired after some public incident at one of the tech conferences (Pycon I believe) where the HR commenting on the firing said something ridiculous like "we reached out to the developer and told them we'd be letting them go". Which I remembered because it sounded like such a massive and rude passive agressive "fuck you"