“How does one even get out of a running car without hearing the engine?”
My guess is that many newer cars, in order to comply with EPA regulations and CAFE standards, default to an “economy mode” in which the engine shuts off when the car comes to a stop, and starts again when you take your foot off the brake. I don’t know if they start again automatically after a period of time. The loaner car I have today does that and it is most irritating. Shuts off at every red light or if you are idling for more than a few seconds.
Now that you mention it my daughter's Honda Insight shuts off at red lights and you can't hear it. It also shuts off the A/C which is intolerable. But I would still turn the car off when getting out.