We don't get enough pressure on the QB to force enough poor decisions and errant throws.
To counter RPO plays, our LBs sit back and don't meet the line or running back until they are 3 or 4 yards downfield.
When the play is pass, we have 3 or 4 LBs in "coverage" that just take up space, not really guarding anyone. It is too easy for a QB, that feels little or no pressure, to complete passes in the coverage gaps.