Question

What all river do not form delta at its mouth

Answer 1

Because of the surrounding geology and the river’s flow. Because of the nature of the seas into which the river is flowing.

To form a delta you need to be carrying a lot of suspended solids that can preciptate out and form banks, and the surrounding terrain needs to be low and yielding enough to accommodate the river changing course. And the banks built up need to survive the storms in that particular ocean