Could be a number of things going on, one would require a bit more information about the fish community and the history of the lake(s) in question, but I can offer some generalities.
It's not unheard of to see stunted populations of walleye in small lakes, particularly where it's an introduced population...introduced predators in small systems can rapidly deplete the natural prey base. Walleye can be pretty variable with their growth and age at maturity...populations under stress tend to reach maturity at a younger age and smaller size than in healthy populations, so we might expect such a stunted population chug along for quite some time. But walleye are also highly cannibalistic, especially when no other prey is available, so eventually the population could be reduced. Add to that competition and predation from pike, which seem better adapted to small lakes in this part of the world, and eventually you could see the stunted walleye population disappear altogether.