Israel has been banging on about range and payload since the inception of the program. Its desire for an advanced version of the F-15 also predates the Saudi purchase (NB the F-16I). The release of the advanced configuration of the F-15 to Saudi just rubbed salt into their wounds. in their eyes they have a demonstrable need to fly large distances, with a large payload, in a self-escorting fighter.
Of course when the Israelis talk about buying stuff they tend to gloss over where the money comes from.