Mostly because last night seemed to be a confirmation of season long tendencies: losing record at Fenway, losing record vs teams above .500, bad baseball luck (3 run HR by the pole), fielding issues, lack of timely hitting (RISP), short run by the starting pitching followed by a good run through the bullpen only to finally succumb to the weakest link in the bullpen, essentially lose to a bases loaded walk , solo HR's not 3 run jacks, etc. This game had it all and displayed to all observers what has happened all year.
In reality with 69 games to go, the Sox need a 40-29 record to hit 90 wins, 18 below last year's record. I don't think the evidence is there to support 90 wins.