Hey TJ, when humans go to a nursing home, they have ample food to eat correct? Yet many of them lose quite a bit of weight and even get shorter...
Me thinks your original bluegill may simply be getting older. Fish don't stay in their prime on the other side of the hill...

The real key to a sustained fishery in a pond is always having the next class right there to take their place.... Many ponds can grow the originals good, but the 2nd and 3rd and subsequent generations that follow typically don't ever compare to that first generation...

That's where pond mgmt practices need to focus on is growing the fish born in the pond or continually stocking and nurturing.... Nobody really likes too manage for the little guys though...