Have a lot of theories but whatever the reason, they are there, ask bass fishermen.
Imo there could be a tie to stocked fish, raised in weedy shallow ponds, it’s natural to how they were raised to be shallow and feed shallow.
Small gils are a common denominator in nontypical, shallow, weedy, more bass/sunfish lakes. Even on typical up north, sandy, rocky, classic walleye waters, there’s shallow fish all spring, summer, fall long.
And it’s not just small walleyes. Have individual lake pb to that lake on multiple lakes that are mid to upper 20″ fish. Biggest on the pattern is 29″es for me and the fw.
The bite windows come and go and at times there seems to be triggers, other times, they just get going for no obvious reason like low light, cloud cover, wind picking up, storms approaching, etc.
A small jig/minnow/crawler/leech, shallow crank, lipless gil colored baits, plastics, spinner baits of all kinds, large willow leafs are personal favorites, slip bobber rigs, split shot rigs, etc all can be effective.
There’s usually lots of void stretches of water, then areas that seem like there just shouldn’t be that many fish, that shallow, in that area. Doesn’t really matter what we think or why the fish are where they are, but if they are there, it is an extremely fun way to fish. It feels more like bass fishing, with a panfish twist. Have 5 kids and the multi species that can be caught doing it can make for a fun day on the water. City/metro lakes have a lot of shallow eyes and imo its because of lack of classic walleye food, on classic walleye structure.