why remove lens on go pro 5 black

I've just bought a gopro hero 5 black and two underwater jackets from different manufactures. I see with the official jacket, the front lens is removed before fitting in the housing. The camera fits in the two "copies" without removing the said lens. Is there a disadvantage to not removing the lens? I would have thought it would make better sense to keep it attached to maintain the cameras waterproof credentials.

Thanks.

My assumption is that it provides a wider angle since the front lens is so much closer to the house outer "lens". This provides better image quality, or at least a wider angle. I believe the house will provide some splash proof even without the cover - and if it's a massive leak, the camera is toast in any case.