They are just not that sanitary. If you are using valves for brewing you really need to go with the butterfly valves. In my opinion there is no substitute.
Even with the cavity filler? I hate all the ball valves I've owned and replaced every one in my brewery with diaphragms or butterflies, but the cavity-filler versions seem like they'd at least be a massive step up on the standard ones even if not as good as butterflies or diaphragms.
And for the little extra bit of PTFE it doesn't seem like they'd be significantly more expensive to manufacture?