Because it is tech stuff related to DVD quality. The general movie discussion forum is almost invariably about the content of a movie, the screenplay, the use of CGI, etc. It is about how a film is percieved by the viewer, not how it is made. Directors are being discussed, the aesthetics of a movie are discussed, even box office performance is being discussed, but never the tech stuff (which is what interests me more than everything else, but that's me). Have you ever seen a post in the general movie discussion forum about why so often in a dialog you hear a person start talking off camera, then the picture follows? Why doesn't the cut occur exactly when the person starts talking? I know why (the editing considers how our brain works), but not what is the recommended timing in what situation. And when the reaction shot should occur. This is just a small example of stuff I am very interested in (among general film discussion of course). Same about lighting. Why are some movies of the 40s, 50s and 60s lit in such a beautiful way - and why are many movies of the 70s a lit in such a shoddy way (everything bathed in white unnatural light)? I never read anything anywhere about it. I would die to learn more about these things. I see people in general don't seem to be interested in that or at least don't post about it. I respect that. So any of my "tech stuff" will come here until someone tells me otherwise. This is just trying to do things right.
As soon as I am in doubt, I'd rather post here.
EDIT: to sum up my ramblings: I am more (but NOT exclusively) interested in the cinematographic aspects of cinema than in screenplay. That's why I can enjoy movies like Koyaanisqatsi, which might be for some other people a chore to watch.