There are a few possibilities here....with several 10 pound plus cats, they were the top predator and could have wiped out all but the largest bass, with adults dying off from old age and starvation since BG are too big for them to eat also. Most likely though, there are tons of 8" bass and no BG getting over 4" long.
A lot of fishing needs to be done to get a better idea of what is there...using live baits and worms with larger hooks and small hooks to target all size ranges. Cast netting would help, so would lowering the pond to a few feet and cast netting/seining or fishing.
