It has been a topic of endless discussion why Ambedkar in the constitution of India Article 1 said 'India that is Bharat'. A clue could lie in this passage:
“If Hindu Raj becomes a reality then it would be greatest menace to this country. Whatever may Hindus say, actually it does not make a difference that Hinduism is a danger to Independence, Equality and Brotherhood. Thus it is an enemy of democracy. We should make all out efforts to stop Hindu Raj from becoming a reality.”
( Pakistan or Partition of India, Page 358)
Ambedkar knew that India is not Hindustan and wanted to prevent any such claim... as is now being claimed that Hindutva is the same as 'Indian' and 'cultural nationalism'. 'Cultural nationalism' is facism, borrowed from the Nazis by the fathers of Hindutva V D Savarkar etc.
The 42nd amendment put paid to any hope of a theocratic Hindu Rashtra, by adding 'secular' to the preamble.