Chennai SSPN was introduced to SBC 150yrs back as weekend express Friday from Chennai and Sunday from Bangalore. Later was extended to SSPN about 10*yrs ago to serve Chenai Bangalore and SSPN as well as intercity for SBC. RSA have come later and the date of operation have changed to Sat in recent years. Even now major traffic will be from SBC only and cannot be avoided.
Regarding LTT CBE is also the same case where it serves to both LTT and CBE. Agree with you SBC needs a daily SF to Mumbai. Is Gauribidanur Devenahalli Sanctioned any project status ?