A lot of these upscale communities pay actual money to stock their lakes and ponds with fish. (It’s not just for fishing - if a pond or lake has no outlet to another major water source, it can get scummy and unslightly, so the fish help balance the ecosystem and keep the water clean.) The members of the community definitely know who lives there and who fishes regularly, and claiming a family member lives there and gave them permission isn’t enough. Kim and Dalton obviously don’t belong there, so fishing from those private lakes is technically theft.
It sucks for Kim and Dalton, but to be honest, they are the kind of riffraff that these rules are meant to keep out. Druggies and low-class people of all ages come into a community and want to use its resources, that members pay a lot of money for, for free. They leave their trash and drug paraphernalia and usually a condom or two. There are places that Kim and Dalton could have gone fishing for free or a low cost, but clearly they didn’t want to do the work to find those and preferred to hit up private property instead.