Looking at that angle, nobody is really open. Singletary had just released from his block and seemed more like an emergency option if the play breaks down. Davis and Allen are obviously not on the same page of where the route is supposed to go. Even if Allen throws a perfect ball where Davis was going to be, it has to be high and very hard or over Peterson which would have been a very difficult throw even with a perfectly healthy elbow.
I blame the playcall first for being too aggressive. There was plenty of time to pick up some easier yards, but the play seems to be designed to go to the end zone. Then I blame Allen for forcing it when nothing was there. To be fair, he had just run like 50 yards and it was the end of an extra long game, and he was in a hurry. These guys aren’t robots, that sort of thing affects decision making.