I'm not sure but Dolby Atmos might be responsible for some of it. Dolby Atmos lets the engineers assign coordinate values to each "sound object" in the scene, then your receiver takes that information, along with the room calibration mic info and your speaker layout, and actually generates the channels itself based on the listeners position within the scene. As an example, if an object is moving from front to rear then the engineers no longer have to pan it between channels, just tell the coordinate system that the sound is moving "that way" and let the receiver take care of it. Maybe engineers just aren't putting as much work into making discrete channel audio mixes anymore when the "gold standard" no longer uses discrete channels/tracks.