It would send a wrong message to the other players that despite them putting in the required work, others who haven't will be picked before them.
And yes, it did send the wrong message to Stack (who incidentally has a history of being out of shape and has poor training standards - refer to Stig and Caesars training notes). If we keep rewarding Stack with games when he doesn't apply himself, how on earth can we expect him to learn about the fitness requirements of being a professional AFL footballer?
And Dimma showing why he's a master coach with his handling of Stack? Yeah, it was great - Stacks form was so bad that it played a major part in our losses earlier in the season. Losses that are accentuated in a shortened season and could cost us a finals spot.
BTW, Balta by his own admission came back in poor condition but was made to earn his spot back and look at him now. Same deal with Eggmolesse-Smith.