Because they're not fools.
Israel want them to take refugees so that Palestine becomes drained of Palestinians but countries like Egypt see the ruse.
Many Egyptians fear opening up the border to all Palestinians instead of sending aid into Gaza would allow Israel to permanently reoccupy an ethnically cleansed Gaza Strip and push the burden of a refugee crisis onto Cairo.
That's what Bibi want , to have all Palestinians leave so he can claim all that prime Gaza waterfront property.