Ram probably wants to "cover their butt". Turbo cool-down is universal with diesel engines. Kind of makes me wonder why the topic does not come up with gas engines???
I almost never "cool-down" in normal city/highway driving. Think the variable speed operation pulls the turbo down during operation. Now pulling on an interstate is a whole new thing. That turbo is most always spinning hard, fast and hot. For all my diesels over the past two decades, I would let them idle if I stopped at a rest stop or anywhere I stopped.
Even just a minute or so would be nice to let things settle out from a long, hot pull. Normally I lock the doors and leave the key in the ignition, engine running.
That's why we have insurance and I also know Samuel Colt.