There ismore to a water filtration housing than the filter inside. The suppliers of these containers want themclear so that the end-user can see when the filter needs to be replaced. They also want to secure the lid with a simple half a hand turn.
This container also has to pass the NSF (National Sanitation Foundation) specifications. These include pressure tests of 400 psi for in-home systems and 500 psi for outdoor and industrial applications. Then all must pass 100,000 life cycle tests at 150 psi.