I’m a BP&W diver for many years now ad I agree there is no better BC from a performance standpoint than a BP&W that is properly set up for an individual diver. That said... there are many times it just doesn’t fit the need of the diver.
First is a new diver that hasn’t yet tweaked and tuned for optimal buoyancy. A standard jacket style BC w/integrated weighting allows them to feel difference they make in where they place weights with limited options. This actually helps in the future if they switch over to BP&W with greater weighting choices. It allows them to better access the changes they make in their weighting systems choices and it’s effect on their buoyancy.
Another place that a BP&W may not be optimal is in a travel rig where size and weight is a consideration. Many BP&W user opt for a light weight BP with a minimal lift wing. IMHO wings of less than 30 lbs lift leave little margin for the demands of a diver as a buddy in a rescue scenario and should be avoided. Many BCD manufacturers have models that meet the demands of travel yet have respectable lift figures in a back inflate design that are better suited for the situation.