No, private sector banks were not blameless; nationalisation was inevitable

Bank nationalisation was not driven by leftist ideology but by a sense of drift in the country and by banks dragging their feet on serving rural areas

Few people understand this but the banking problem in India after 1947 has always been a political one. So it is a mistake to treat it as an economic or commercial problem.

At the heart of the politics lies rural credit, and its origins go back at least 500 years. If you read India’s economic history you will find that in the 1950s, rural credit and irrigation, rather than technology and better practices, were seen as being critical. 

The policy was this: while irrigation would be taken up by the central and state governments the problem of credit to farmers was intractable.