This is all speculation on my part based on a growing number of complaints I've read and responses from people in the industry. For TV it's due I think to higher level consumer technology - 5.1, 7.1... 22.2 ??!! surround sound are much more affordable now. The teams responsible for both the audio and video are aiming their output to look and sound superb at the highest level of tech available so they'll pipe virtually all speech to specific channels and effects and ambient sound to the rest. Since at least one channel is dedicated to speech - with a well balanced system - dialogue and effects really ought to be clear and audible and lots of people report that. I bet the majority of people are watching TV with stereo sound though and the audio engineers either weren't paid to make a separate stereo mix - forcing your TV/laptop/phone whatever to automatically mix down for you - or they did make a mix but don't have the time/budget to test that mix on the bottom 70% of equipment that most people use. I made that figure up from this article that projects 40% market share for home theatre systems by 2023