Cause no one ever retaliates when struck by acts of war. If you think all wars are nice, neat, and contained like that nice little bubble in your head, think again.
You read those facts in spite of what he was trying to do. You only look at what he was backed down, forced, into doing. He did not have popular support, he did not have Congressional support, he did not have UN support. Obama stood alone.
After the fact, yes, he couldn't go with the "shot across the bow" and why do you think that is? The world forced his hand at peace in spite of his best efforts to drum up support for something no one but the Neocons wanted.
Obama will get credit for not preventing peace, but he gets no credit for striving towards it. That credit will go to those who opposed his war effort.