The Curious Incident of the Pass On the 1st Down

Passing is king in the NFL, but did the Super Bowl Champion Philadelphia Eagles exploit a market inefficiency on 1^st down or did they pass a threshold that limits their efficiency? The eternal debate concerning run:pass ratio is one the football community will likely never settle. If passing is king, why do teams continue to run at a higher rate on 1^st down and 10? If the success rate is higher for passing in that situation, it would stand to reason that more teams would make a hard shift in that direction.