As far as I'm concerned there's only one real reason why auto-pass can't be done and that's because the original design didn't allow for it. The method of dice-rolling is to roll them when the user accesses the page. This precludes auto-pass.
Sites that implement auto-pass roll the dice at the first opportunity. At GoldToken, for instance, if you make a move and then visit the game (non-cube) page immediately afterwards you will be able to see the dice that your opponent will be playing - whether they're online or not. By rolling the dice automatically the system is in a position to skip the move if necessary. At BrainKing, because the dice are rolled only when the player visits the page, there is no opportunity to skip the move. I reckon the changes required would be quite considerable, hence auto-pass is not an option. Any other reasoning for auto-pass being BAD is spurious.