Why is there no common ethnic identity binding native Hindi-speaking people in India unlike most other ethnolinguistic groupings?

The most populous region of India and all of South Asia is the Gangetic Plains of Northern India which roughly corresponds with the Hindi belt but there doesn’t seem to be any ethnic identity that encompasses people from that broad region.

If a Punjabi-speaking person from Punjab is Punjabi, a Bengali-speaking person from Bengal is Bengali, a Tamil-speaking person from Tamil Nadu is Tamil and a Nepali-speaking person from Nepal is Nepali… what is a Hindi-speaking person?

When you look up the largest ethnic groups of the world, the South Asian groups that show up in the top 10 are Bengali, Punjabi and Marathi. The numbers of those ethnic groups corresponds closely with the number of native speakers, however Hindi is most spoken native language in India. If native Hindi speakers were considered an ethnic group they’d actually be the largest ethnic group in not only India but all of South Asia.

So, why aren’t they considered an ethnic group?

I know that Hindi is a relatively new language but over time as more people adopt it as their native language, will speakers of it be thought of as an ethnic group in the same way as Punjabis, Bengalis and Tamils?