You don't just take a rest when things aren't going well. So you pay him millions of dollars per game, to take it easy? What kind of message does that send to the rest of the team? You fellas go out there and take a beating, Matthew is better than you so he's going to sit.
Coaches and players don't tank seasons. They try and win every game no matter their record. If they didn't have that mentality they wouldn't be in the league for long. Playoffs or no, you want to build up to the offseason and try and salvage some positives.