His playcalling is a reflection of what JG cannot do. If your QB cannot process information fast enough to burn opponent blitzes then you have to design gameplans that mitigate blitzes some other way. You have to run on passing downs hoping to catch a seam. UT did that a few times vs Bama.
If your QB cannot anticipate throws and has spotty accuracy, you cannot throw to the deep middle against good secondaries. That further limits what you can do in the run game AND puts more pressure on your OL in protection.
There's a ton more... but he cannot call plays that his team and particularly his QB cannot execute... and he cannot call plays that run off those plays either.
A LOT of people here underestimate how much JG's limitations directly and indirectly limit the O. Don't get me wrong. Almost all QB's have some limitation that the OC has to gameplan around. JG just has too many and especially for a RS Sr.