You please check the ticket availability in Matsyagandha and CST SF from Mangalore.Even tommorows ticket is RAC only whereas you check the availabilty in Netravati or Mangala from ERS,it is WL for more than a month.Definitely,the railways don't find the need for a premium till MAJN.Also these special premiums run very slow(speed in 40s) whereas there are two dedicated SF from MAQ/MAJN.So it is better to serve regions with less trains to Mumbai.Maybe there is a Techinical halt at MAJN(I think railways don't announce tech halts like that).We will find out after the train starts running.