If they have great gameplay that doesn't fit in with the story, they have 2 options : 1) give up on it or 2) shoe-horn it in. I've found designing LBP stuff that limiting oneself to a realistic setting makes it far, far harder to incorporate good gameplay. If you ignore all sense and throw in random elements, you have a lot more freedom to create gameplay. In the case of LBP, the whole premise allows that (but my level design doesn't!) and the creators have a lot of freedom. With Gears, the premise is very constricting to gameplay. I guess the developers decided Story was a back-seat priority and through it aside to add Funness.