Too many rounds, too many details, and questioning for long hours, crossing you, so you definitely make some mistakes, and they are all focused, giving pressure in the interview, so you say something wrong or not perfect, and find a reason to deselect. And usually they will not be having hard requirements to hire, but just to keep their employees busy, they always have open position which are not meant to be filled easily.
Do not waste your time with so many rounds of a long interview. Their intention is to make you fail in the interview as you move along.