There is no reasoning; they're just parrotting misinformation they heard from someone else.
As O'BSC said, prostaglandin injection will only 'bring them into heat', if they have a CL on the ovary following a previous ovulation. Estrus following injectible prostaglandin-induced lysis of that CL should be just as fertile as one resulting from normal cyclical lysis of the CL, or, for that matter, one resulting from a second injection 11 days later.
Back in the day, before CIDRs, etc. - and I still do it sometimes - we'd watch for heat for 5 days, breed any that came in in that time frame, then give a prostaglandin injection to any that hadn't shown heat in those 5 days... and anticipate that the vast majority will be in heat in the next 36-72 hrs.