I would guess that the number of people listening to this media on anything higher quality than the built-in speakers on a 65-inch TV is minuscule. They’re optimizing for sound on an iPad, not a full surround sound setup.
I never cared much about surround sound until the AirPods got spatial audio. Now it's like I can't live without it.
As somebody who has a very nice (and expensive) 5.1 set up, I’m legitimately a bit worried about this trend.