Even the Hindiest of the Hindi-speaking people, e.g. in Uttarakhand say "zaroor".

You will only find someone like a Hindi teacher or a priest using a word like "avashya" when they're trying to signal that they are educated and thus speaking in the 'pure' register. In the natural language of Hindi, the word used is 'zaroor'. Using 'avashya' is speaking a conlang, pretty much.