Apparently, because Valve can’t really tell who owns a Mac, they’re just giving all of us preorder customers the Valve Complete Pack for free. This is part of the text from the email I just received:
We’ve added the Valve Complete Pack to your Steam account as a gift from Valve. This will give you all of Valve’s games (past, present and future) free of charge. You can still choose to refund your Steam Controller and/or Steam Link (refund instructions below), but the Valve games are yours to keep.
That’s how I know we’ll never get another regular retail game from Valve again.