@Paul Roberts and I have had some pretty in-depth discussions on this very subject over the years, and it largely boils down to adequate food supply and longevity. These ponds have to produce enough food of various size classes, and it has to be available to the bass at the right time/age Plus, the fish have to live long enough in them to be able to grow big. However, such conditions don’t exist very often in these man-made systems as there is little ecological stability. Many are borderline insufficient depth for survival or protection during severe winters or summer die-offs. They are rarely stocked intelligently/intentionally, and then managed afterward. They frequently receive excess nutrients from adjacent farm fields or home owners yards, then get treated by HOAs for excess weeds/algae, etc. due to this over-fertilization. Plus they tend to get a lot of foot traffic from anglers which likely crop off many of the few big ones that do make it against the odds. It seems like 3 pounds (give or take) seems to be the natural limit before fish start getting skinny and succumb to either insufficient forage (of appropriate size), harsh environmental conditions, old age or fishing pressure. Anything above that size is kind of a special fish in these little waters. Those waters that regularly produce a lot of bigger than normal bass, or have really good overall bass size structure, can probably attribute it to one of the above factors (or more likely several of them) falling into the basses favor (against the odds).