This is weird to me too.
I’m a nervous flier, and the moment we start to make an ascent or descent when we’re at cruise altitude I know it and freak out. You can bet I would notice immediately and have my cellphone out and calling the second I got a signal if we were descending 3,000 feet a minute in the middle of a flight with no notice from the flight deck as to why...
Exactly why I wondered that no one did or they aren't speaking of it.