Earlier quoted context omitted.
Is this a US thing where the company doesn't want to give any reasons for firing someone because that can be used in a lawsuit against them?
I would say so. This video is a perfect demonstration of America's "at-will employment" culture. It's extremely asymmetrical, too. Companies can fire you at any moment, for any reason (with or without cause!)... yet it is considered rude for employees to not provide ample notice when deciding to voluntarily quit.
I’ve lived a very different culture than you in the U.S. - to the degree I’m surprised to see you express this sentiment.
In days of yore, people gave notice. But then a meme policy of “don’t poison the well” did the rounds. Roughly, the philosophy went: when someone is leaving they can only do harm; they are leaving, they have a convincing reason for leaving, and you don’t want that convincing reason to sour your other employees on you.
The result was that, when you gave notice, you were immediately dismissed on the spot.
In my career, I’ve seen a few people give very generous (months) notice. They were expecting to be _paid_ for the period of time they’d given notice for. But they found themselves terminated that day.
The result, in my circles, is that people often hide their intention to leave until the day they’re leaving. When they send their notice, they’ve already quit. Any time they get paid for is gravy, but they’re out the door.