I'd say it's the opposite: people go for the movie, they don't give two damns about the "bonus content" (who does anyway?), so they need to be force-fed with it

I'd say it's the opposite: people go for the movie, they don't give two damns about the "bonus content" (who does anyway?), so they need to be force-fed with it, just like with ads, if they're to see it. As for why do it in the first place, I'd say that "old movie + exclusive premiere of new extra content" may lead some people to choose the cinema over countless other ways they could watch the same movie at home.