Backpedal, why isn't this dropback more popular?

[toffee]

Dan Marino used this technique, Dan Fouts, John Elway, Kurt Warner too. Why isn't it more popular?

 

[IndyHawk]

Dan Marino used this technique, Dan Fouts, John Elway, Kurt Warner too. Why isn't it more popular?

OL has gotten worse over the years and so accustomed to having a QB
use shotgun so much.