The why is not up for debate. "missiles at Syria" is obviously a keyboard macro for this administration. The when is the subject at hand...
Given the above, would you argue that the when of this strike was selected for tactical or strategic military reasons?
This is far more your wheelhouse than mine, but my understanding is that the Joint Chiefs are in charge of strategy but without a formal declaration of war the President has to authorize military force. A set of strike solutions would have been studied and prioritized based on conditions. Once force has been authorized, the strike itself can happen within operational parameters.
Suppose there was a joint strike mission in the works, along with congressional approval, coordination with the Russians and Turks, the whole enchilada. But then yesterday morning Trump tells Mattis "strike Syria as soon as possible." Your envelope is now a ticking-clock optimization between orders from the President and tactical advantage. You won't be getting congressional approval, you won't be coordinating with the Russians and Turks, and you'll be telling the British and French "we're lighting this candle before sunrise in Damascus."
I'll bet the result looks a lot like what we saw.