Dave,
Daddylonglegs are primaraly scavengers so yes, the reason they get caught is that they are trying to take the remains from the traps and trigger them. The pain of it is that usually the trap can not seal around the legs well enough so the trap rots. But the legs hanging out makes for a fun site and if you want to gross your friends show them a recent capture and how it'll stil twitch its legs if you brush them
(Yes I am a sick twisted person.)