In fact S-300 is a yesterday system. It has to be sold by Russia because the Chinese has copied the technology already and would gladly put their version on market. Why give them this market?
The Israeli’s demonstrated that they can “Work around” the system in Syria. We also most likely have a work-around for it.
But do the Saudi’s and Egyptians have a work-around for it?
SCUDs are beyond yesterday, but Israel doesn't want them making their way from Syria to Hezbollah hands in Lebanon.