They also buy lots of guns from the US. This is one of the real reasons. Lockheed Martin’s profit margins would decrease by a significant amount if our relationship with SA changed at all.
Even if the Saudis and other major countries in the reason were able to decrease tensions with Iran, Lockheed Martin and its associated propagandists and lobbyists would start beating the war drums to increase tensions and thus sales.
Edit: *one of the real reasons. Added para. on LM ensuring tensions in the region always remain high even when the people that live there and their government’s reduce tensions.