Because the middle east hates each other as much as they hate Israel. Early on in the immediate postwar period the players were mainly Jordan and Egypt, but today, Iraq, Iran, the Saudis, Jordan, and Turkey all have interests in the region. Not to mention Israel has nukes.
Jordan always dealt with Israel under the table, so it's quite satisfied with Israel, and Egypt has essentially worked with Israel since Sadat.
Turkey and Israel were close allies due to NATO/US relationships. The Saudis are in a similar situation.
1999 Lebanon was (and honestly still is) a mess following the civil war. Hezbollah is actually very impressive for a paramilitary group in terms of its performance against the IDF, but even their members have admitted that they wouldn't stand much chance attacking Israel.
That leaves Iran, Iraq and Syria, only two of which border Israel, two of whom would rather ally with Israel than help the other (Israel supported Iran during the Iran-Iraq War), and none of which realistically have a chance of beating the IDF.
If a world nuclear war started most of the middle eastern nations would be more interested in knocking each other's shitty semifeudal arab militaries out than challenge a modern, partially US-armed Israel with nukes.