That political entity no longer exists, and the people of Egypt would likely never have willingly parted with the many obelisks and other historical artifacts that have left their shores.
1. You need to draw the line somewhere. It is simply not possible (nor even desirable) to redress all historical wrongs. It seems reasonable to not attempt to redress wrongs which are out of living memory for anyone involved.
2. As others pointed out, the people currently living in Egypt is not the same people who lived there when these things were built anyway, and there was a hell of a lot of conquest to get from there to here. This is not a case where the Ottomans stole it from the original owners. That makes this not a very good candidate for giving it back.
The people currently living in Egypt are most definitely the same people that built these things. The Coptic Christians of Egypt liturgical language is a direct descendant of ancient Egyptian and the Muslims of Egypt are well documented to be descended from converted Copts.
