Exactly this! Practice hours are very limited, thus the number of reps, and plays able to be practiced are limited. A coach is going to want his 2s to be repping the exact same things as his 1s, in case they need to step in for an injured player. The way Alabama rotates players and formations, there are probably 26-28 guys who really make up the 2 deep on offense. A coach can't completely change what is going on because one of those guys isn't a fit for the scheme.
Anyone can go look and see I was highly critical of BOB, but in context, he's still not really wrong about his statement. In a pro-style, NFL oriented passing offense, JM still isn't really a fit as a QB. After the UT loss, in film review coaches were asking Jalen what he saw and should have seen that resulted in certain things (i.e. read he was making, or supposed to make) or maybe what he really should have keyed on, and he told them he didn't know. To accomodate, CTR has made significant changes; taking out some routes and concepts altogether, and simplifying what JM has to try to read, and we still have guys wide open in the progression and JM doesn't get the ball there. Many of JM's 'wow' plays actually only happen because he missed the early open reads and then had to default to sandlot football to make something happen.
