Looking at these abandoned lvl 1-15 castles is a complete eyesore. You can't raid them for anything, besides maybe some troop remnants during PvP for injury score. They're just... there. They don't have any other purpose. Perhaps allowing for resources to produce over resource capacity should be implemented. It would also double as a reason to stay active in order to keep your resources below capacity so you don't get raided by other players. Inactives should work as a sort of source of resources, rather than being some sort of decoration in the realm.
They eventually remove certain castles from the realm. Turn your phone sideways to landscape mode and click the letter ‘A’ in my signature to jump to a definition for ‘account hibernation’. The accounts that you are seeing are ones that have spent real life money on the game, in which case they will never be removed, which kinda makes sense? But I agree that they should be removed too, eventually.