For a technical reason involving contact patches on the fingers inside our switch, once they work, they continue to work. They might fail to start you up, but once the engine is running, it continues to run.
The similar but not identical incidents especially with other GM vehicles is a mechanical problem with the root cause being an easy-to-rotate key cylinder, combined with too-heavy keychains acting on an ignition key with a SLOT in it for the keychain to pull on the downhill edge of the slot, combined with a design that puts the key horizontal when it's in the RUN position. If the RUN position wasn't horizontal, but vertical, a too-heavy keychain couldn't rotate the ignition switch off as it pulls at the bottom of the slot. If the key had a centered hole instead of a slot (one of GM's countermeasures) the keychain couldn't get any off-axis force going to rotate the cylinder off. If GM had kept the airbags active for a short time after the ignition was turned off, they might have acted to save a few lives even if the driver didn't figure out that they engine had gone off due to the key rotating backwards.
Then GM redesigned the cylinder to increase the detent force, but they KEPT THE SAME PART NUMBER, which was insane, so mechanics could never tell if a vehicle bad the updated cylinder or not. And the usual coverups, worry about cost by the bean counters, and the inevitable debate of the value of a human life to a corporation that values the stockholders more than customers or bad press.
It reinforces my old thought that (if I was ruler of the world) nobody could own a vehicle if they couldn't demonstrate they could steer and stop it safely IF THE POWER ASSISTS ALL DIED. You wouldn't have 89 pound elderly folks sitting on a pillow behind the wheel of 8000 pound Coupe DeVilles. Sorry - no matter how rich they are - they get Aveos. It's one reason we don't have steering wheel locks anymore - sometimes drunk or irrational passengers take the ignition keys out while the vehicle is moving, against the will of the driver! Losing steering due to a lock bothered the lawyers enough when they thought about it, that the benefit of a lock for theft prevention wasn't enough to make up for even one accidental death.