Every airline operates their respective jumpseats the way their jumpseat committee, and or management wants. Example: American Airlines has both unlimited jumpseat agreements with carriers reciprocating unlimited, and limited with those that don't. Same with international agreements at AA. AA's management will not allow international agreements with carriers that don't fly internationally (exception SWA) regardless of CASS.
Others airlines ONLY accept CASS carriers to their list (i.e. FedEx). Here at SkyWest, we accept CASS and non CASS, but you HAVE to be on our reciprocal jumpseat list. It is just how different airlines operate their jumpseats.