Why does my Apple Watch Ultra 2 pause if I stop moving on an outdoor walk, but not when I'm going 70mph?

When I start an outdoor walk on my Ultra 2, it pauses if I stop moving for too long (which makes sense).

But if I forget to pause or stop it before I get into a vehicle, it keeps going, I drove 7 miles and 50 mph+ and it never paused or suggested

[Re-Titled by Moderator]