I seem to remember that they started fading out once they got into direction. I mean film direction not just MD-ing. . Ofocurse their film flopped (jagathalaprathaaban, *ing mohan), but I don't see why that should be a reason for them to leave the music arena.
They probably thought that since there is a person who follows their style of music making (you know who) and is better at it than they were, they should leave the scene.