"Key not in the car" should be condition enough. I'm having a hard time thinking of a scenario where you NEED to have the key away from the car while the engine is running.
It also breaks the backup mechanism for no-battery situation where you can tap the fob on where the ignition lock would be for key cars to start it up.
Those people don't need to take the car key with them, but with a keyless car you don't think about the key (that's the entire point of keyless cars). The key is just one of many things in your pockets.
For animals that's different of course. But wouldn't an override be enough?
This was in the late 80s. The car wasn't running. It was a mechanical e-brake. I know a lot of cars have electronic parking brakes now, but most probably still don't.
On another note, I can't think of a single car that will let you take it out of Park without a foot on the brake, or without using an override.