need to get. The chance of success in those circumstances is much lower than when the defense isn't expecting it. (The long pass play to Blackmon happened because the secondary bit on the play fake and the threat of a pass out to Houk in the flat. No way that happens on 3rd and 27.)
Sure, something good might happen if Taysom hails back and lets it fly, but something bad could happen just as easily (like a sack or an interception). Most OCs would call something similar--a draw play or maybe a screen in that situation.
Now, one other option that might have worked better would have been a QB draw. Have Taysom drop back, survey the field, then take off. But other than that, handing it off to Williams was among the best of the bad options available to Anae.