Another big difference between Crappie and BG is that Crappie spawn very early AND unreliably.
The early spawn means that baby Crappies get first dibs on everything else hatching in the pond, often to the detriment of both forage species and bass.
The unreliable spawn, caused by varying environmental conditions that early in the season (IIRC), means that Crappies themselves are not reliable forage year in and year out for bass.