SWR trains run deep into TN and KL like CAPE, Trivandrum, Ernakulam, Kottayam, Calicut, Kannur,
Coimbatore, Erode, Madurai, Tuticorin, Puducherry, Mayiladuthurai, Trichy, Thanjavur, etc. Even a passenger from Bangalore runs upto Karaikal and southern railway does not run even one train to connect Salem to Cuddalore Mayiladuthurai Thiruvarur Karaikal.
How many SR trains operate/ terminate at SWR destination? Practically zero. So, it would be better to run SR trains to SWR area passing through Bangalore.