Question re short yardage defense

[ForCuseSake]

In both games this year our opponents have had 4th & 1s and snuck it up the gut for a 2-4 yard gain. In both situations I remember seeing nobody lined up directly over the center - practically begging for a QB sneak. My question is why don't we line up in some type of goal line defense instead of our base D simply crowding the line with nobody over the center. Not an Xs and Os guru so correct me if I'm wrong.