Tummbad also profited because of good reviews and word of mouth. Kantara did good in box office because it's a regional movie. People associate movies of their state with pride. So they will not only watch it. Heavily promote it as well.
I used to watch spiritual movies & some old thalaiva movies on zee cinema from south in hindi dubbed long before sony max mass & star gold shivaji. Zee started this dubbing saga. But the extravagant promotion is done by Sony Max. No one can deny the contribution of sony max in promotion of south movies