I also don't see why, if an employer demands a pay history, the candidate is obliged to provide it.
(And also, in my experience, nearly all candidates inflate their salary history by about 10%. Employers know this, and discount the salary history by 10%. Back when I applied for jobs, I provided a pay stub along with the comment that I wasn't lying about my salary.)
Not having a clue about what a candidate formerly earned means risk for the employer, and risk always means that the offer will be lower to account for the risk.