I believe in the case of LO it is a forage base thing. There's simply nothing for mature bluegill to eat. The winter drawdowns effectively kill off mosquito larvae (we know that for a fact). Also most dragonfly and damselfly larva/nymphs are exposed-dried out-frozen as well. The same reason that LO has no FROGS is the reason why it has very few mature bluegill. There simply isn't enough food to sustain them through numerous growing seasons.
If they were to halt the extreme winter drawdowns then a more healthy population of bluegill would eventually come back. As would the aquatic insects, frogs, and the milfoil.
Crappie have a major advantage over bluegill on this lake simply because of the size of their mouths. A mature bluegill just can't quite make a living on plankton, and he can't fit a 2-3" shad in his mouth.....so he only gets to chow down for a 2-3 week period, once per year, during post-spawn. It's a long LONG wait between good solid meals.
Back in the days of styrofoam dock floats they (General Electric) were not in the practice of drawing the lake down nearly as low. We had milfoil back then too... because of that. Milfoil and aquatic insects can't survive here anymore because of Ameren, who has effectively eliminated it/them via their more extreme winter drawdowns.
Listen to me, sounding all like a fisheries biologist and $#!t. 🙄