I think you answered your own question. They weren't going to switch to Curry, who has not called plays in NFL games before, with the playoffs on the line given that Carmichael and the offense were much improved in the later part of the season. If the offense was still struggling in the last 5 or 6 games then sure give Curry a shot, but it was actually working with Pete calling plays late in the season. So, I'm not sure that the final decision was made on Carmichael until after the season was over.