It's a lot easier (and honestly quite savvy) for DL to do this. AA and UA are (far) more popular for Members or Congress because of the hubs at DCA and IAD. These special services desks are really not costly to operate and well worth it to avoid unpleasant experiences from customers who are more important to AA's bottom line than CKs. Keep in mind, House and Senate ethics rules prohibit the airlines from comping elite status for Members.