That sounds like a wild-assed guess.
Truth is, they really don't know - they need TIME to investigate. Re-writing code to integrate into existing code requires analysis of ALL of the existing code - in order to see WHAT needs to be re-written and HOW it can be re-written so that it can be seemlessly merged with the existing code. Its like forging the Mona Lisa - you have to study the brush strokes BEFORE you start the forgery ...
And, SOMETIMES, it can't. You just have to scrap the original code and start all over.