cess is meant to be used specifically for the specified purpose. like sbc is meant to be used for swachh bharat and similarly for kkc. In general taxes are distinctly collected so as to bifurcate the revenue of central govt and state govt
But instead of charging each thing seperatly can't amount be allocated in budget to SBC and Kristi kalyan and my other doubt is why credit is allowed only for kkc and not sbc
simply because it is specified in the notification. however, government issues such notifications based on severity of subject matter. there can be other criterias too.