I�m not an expert by any means.
My guess, if there�s a lot of open water with good depth and little vegetation bluegill recruitment maybe low. Redears favor deeper water than gills.
I would guess if gills only spawned once, like they will if they don�t have the food they like, redears could have a bigger spawn and out produce em
I have a friend that thinks grass carp raid nest while they graze.
I�m just throwing out ideas