Here's why:
* Popularization by Bhagat Singh: While the phrase might have been used before, Bhagat Singh's use of it during his revolutionary activities, particularly in the 1920s and 1930s, made it widely known and popularized it as a rallying cry for Indian independence.
* No definitive proof: There is no concrete evidence proving Bhagat Singh's sole authorship of the phrase. It could have existed in some form before his time.
* Evolution of the phrase: The phrase itself likely evolved over time, with various individuals and groups contributing to its usage and meaning.
Therefore, it's more accurate to say that Bhagat Singh popularized "Inquilab Zindabad" as a revolutionary slogan rather than solely coining the phrase. The term represents the collective desire for freedom and revolution within the Indian independence movement.