The United States (US) has long been an ally of Israel and to a lesser extent Saudi Arabia. I believe the US and the Saudi’s relationship first started to develop after World War II when the two countries started talking about Saudi oil in exchange for military, technological and economic help from the US. Now both Saudi Arabia and Israel are working towards building an alliance against the regional "common threat" of Iran.
Egypt, Jordan, and the Gulf states, excluding Qatar, are also dealing with threats from Iran and radical Islamic terrorist groups. Israel is known to have a military, nuclear and hi-tech expertise unmatched by other Arab countries in the region. So, Saudi Arabia has decided to become better friends with Israel.