Genesis 50:6

And Pharaoh said
To Joseph, by the courtiers that waited upon him at Joseph's request, who having delivered it to him had this answer: go up, and bury thy father, as he made thee swear;
the oath seems to be the principal thing that influenced Pharaoh to grant the request, it being a sacred thing, and not to be violated; otherwise, perhaps, he would not have chosen that Joseph should have been so long absent from him, and might have thought a grave in Egypt, and an honourable interment there, which he would have spared no cost to have given, might have done as well, or better.