That's actually close to another very important point. Most movies come with a 5.1 mix nowadays, and people watch them on a stereo system. Most players use a very simple formula when converting 5.1 to stereo, something like say Lout = 1/2 Lin + 1/3 SLin, Rout = 1/2 Rin + 1/3 SRin, and leave out the center channel completely. This is also done inside of TVs etc. The center channel gets dropped completely! And sometimes dialogue is only in the center channel - not all of it, but there are some lines every now and then that just only ever come out of the center channel. Those are lost.

This sounds too stupid to actually be true, but it also seems to correspond to my experience. It makes me sad that there's an engineer or produce designer out there, anywhere, who would intentionally pull something like this. It's sadistic. Why ruin your product?

The issue is that most programmers think there's nothing to know about the non-programming-related engineering they're encoding into their programs. So we get crappy audio, we get cars driving into bollards, delivery robots driving over crime scenes, home automation destroying houses, smart locks that can be picked without tools, etc. People severely overestimate their knowledge of what's going on, and underestimate how much complexity there is to the phenomena they're dealing with.

Are you sure? I thought a lot of people were successfully running "phantom centers" by just using L and R

If the information from the C channel is dropped, and the speech information was only in C or for the most part in C, it won't be in L+R, or it will be to some insufficient extent because it'll get obscured by whatever else is happening.

I have a home theater (do they still call it that?) with 5.1, 5 speakers and all that jazz. I tried everything but with many movies (esp. all the superhero stuff) the only option is to lower the volume and turn on the subtitles to be able to follow the dialog. I wish there was an option to make the loud parts less louder and quiet less quiet, but I couldn't't find it (it's an older onkyo).

Dynamic Range Compression. Pretty much every HT system has had it for 15+ years.

I'm going to guess that most folks now-a-days go with a single soundbar that acts as the whole sound system, maybe there is still a center channel in the bar? Whether that be for; price, small living space or a partner doesn't want speakers around the world, its a convenient space saver that sits under the TV, sight mostly unseen.