Because the combat arms guys who actually do the fighting, killing and dying overwhelmingly oppose it might be a reason to be surprised.
They might be outraged, they might be saddened, but I can't imagine anyone serving today would be so clueless to the shifting political winds as to have been surprised.
For crying out loud, I knew it was a foregone conclusion the moment Obama was sworn in. The only thing I'm surprised about is that it took this long.