Most of the time sound engineers also make a stereo mix, with significantly less dynamic range.

Blame your TV/computer/whatever-screen for going technically a multichannel surround system could be plugged into me at any moment, I will tell the streaming-service/Blu-ray/DVD/media-file to feed me that sound track! Switching to the stereo track makes a big difference, but yeah, for some reason the surround track becomes the default option.