Because passione produced a subpar season (DxD Hero), while you may be able to bash TNK for the last season (BorN) and their decision to cut content from it plus the pacing being all over the place, passione did no better in their first attempt plus while more faithful to the LN the art style was also lost and downgraded. Overall I don't think Passione did a good job, personally I would've gone with a different studio tbh. TNK was out because they couldn't shoulder it financially anymore either.