I'd say it was conservative play calling.
Lemme ax yuse a quesshen.
You're the OC of the Dallas Cowboys (or the Head Coach). You know you are facing a depleted secondary, featuring Loan Security Officer Ralph "Pete" Hunter.
On the first play from scrimmage, why on earth do you not spread the defense with a 3-4 WR set, and send all 3 WRs on fly patterns, or deep seam routes?
Even if you don't complete a pass, you scare the bejesus out of them. They immediately go into a conservative protect formation. Throw a few more deep patterns and maybe complete some, and guess what?
The ExLax factor kicks in.
The holes open up in the middle of the field for Julius wider than he's ever seen.
Instead, what do we do? Try to establish the run right out of the gate and throw a few short passes. Pretty soon old Ralph looks like Deion out there, and the coaching staff gains confidence in their coverage abilities enough to play a bit more aggressive against the run.
UGH!