disagree with the people who make the DVDs. :)

>When they make the film, they manage to free up several
>thousand hours together. For the DVD (which these days
>generates more revenue than the theatrical film) they can't
>find two?

And it takes more than two hours. Depending on how in depth they want to be, it's easily a full day's work.
And they aren't always in the same city.
And it's recorded months after the movie is done, on a (usually accelerated) schedule all its own, regardless of what the principles are doing.
And despite how much money DVDs make, none of the suits involved give a shit about DVD commentaries.
And so people doing the commentary don't get paid anything extra.

Don't misunderstand. I'm not sure how widespread this separate recording is. It's certainly not done all the time. But these are perfectly plausible reasons why they would do it separately. And those reasons aren't going away any time soon.

RED
Ora et labora