Really think it's difficult to blame Reyes on this one, seems more like a split-second decision that went poorly.
Assuming he did have the wherewithal to contemplate his decision, perhaps he was thinking that going in standing up was the best way to avoid injury, and then realized he wasn't going to make it. Kind of like pitchers trying to barehand a comebacker; they likely don't think it's a good idea, but instinct kicks in.