We have two rivers flowing in the western ghat NARMADA and TAPTI.It flows in the mountain region of VINDYA and SATPURA  which cannot have alluvial soil to form delta as it requires sediments to form DELTAS.I think this could be the only reason and may be if some one has better understanding can post the answer so it will help the students
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Delta are formed when the flow is high and sediments are deposited.but in the western ghat the flow is not high..