Olympus LR-2 Rear Lens Cap For E-P1 Lenses

I have an Olympus PEN E-PL2 camera. When I got it, the kit lens came with a smaller rear cap that covered only part of the rear and was difficult to put on and remove. I first came across this cap when I purchased a secondhand lens. I like it because it covers the whole rear of all my lenses and is much easier to put on and remove. Why didn't Olympus just give us this cap from the start? Why do we have to purchase it as an extra?