I've only truly realized in the past few days that Apple's "Vehicle Motion Alerts" are actually to prevent motion sickness.

In the past, when sitting in a car and looking down at your phone, it was easy to feel head pressure and nausea, making you think you couldn't handle it. After enabling this feature, the edges of the screen subtly move with the car's acceleration and deceleration, making it easier for the brain to judge direction. Looking down at the screen isn't as uncomfortable anymore.

This design is interesting; it's not to make you aware that you're in a vehicle, but to quietly reduce discomfort. Many features work this way—when you first see the description, you might not notice it, but after using it for a while, you'll realize it's silently taking care of you, saving you from small, habitual discomforts.