Let's put this in perspective.
There's a limit to the number you can take on the road in SEC play: I believe it's 65.
Minus three kickers.
Minus three quarterbacks.
Let's just say we have 60, divide by two now we have 30 on both sides of the ball.
In the third when you mentioned this I had seen over a dozen play combinations on defense alone. We've been playing back-ups since early on. But, not in a few positions IE: Quarterback.
BUT, when you are playing kids at WR who are realistically our seventh and eighth plus guys off the bench you want those kids getting reps with the starter. Same thing needs to be applied when considering who is on OL with the back-up QB.
It's not as easy as "we're up by 35, let's mass sub." There's still seven SEC games left, plus post season. They need the time.