I was wondering why don't developers of AAA games release their source codes after their game has sold out and support is long gone?

Of course there is this list, where you can find a lot of AAA games with available source code.

I just don't seem to understand why don't other companies do this with their old games? They certainly don't support it any more, and sales are negligible. I am not even sure, if releasing the source would negatively impact a games sells.

I am sure a lot of games, that are doomed by gamespy's closure, could be saved by the community, had their source codes been released.