Uh, it isn't. GERD's operation's negative effect on the Nile's yield are minimal, and they could be even positive with coordinated, basin-wide, water management, but that's something Egypt has been continusouly against. They've never really looked at the other nine/ten as equalls...

The problems are that the Nile is a modest River and that Egypt has a population problem in a resources-strapped region, coupled with extremely unsustainable government policies (a topic in itself is an amalgum of compounding issues).