She is nowhere near Aish in terms of beauty or aura. Even though Aish is not a great actor, she has a thing called screen presence. Hence Sneha failed.
I think you have your answer right there Because Salman was backing her.
And he lost interest eventually.
I can't think of anyone who was launched by him other than Katrina Kaif who had a proper and long lasting career in BW and even then she debuted in a movie where he had no part in, the rest either make a guest appearance or disappear into oblivion. Contrary to the general belief, The man really ain't that lucky for the people he launches.