The reason why they wont create a so called 'Nato' against Israel is because nearly every arab country is a US/western puppet so Israel is pretty safe. Heck even Egypt the biggest Arab country is helping Israel blockade Gaza, While Jordanian president openly walks alongside Netanyaho and gulf states secretly share intel.
Another important reason is that arab leaders are natural backstabber and hypocrites and plot against each other. Half the arab world is destroyed and the other half helped destroy it. This is why even tho Arab countries are US puppets, they still cant form a so called 'nato' To fight Iran.
Quran 9:97 The Arabs of the desert are the worst in disbelief and hypocrisy, and are least inclined to acknowledge the limits that Allah has revealed to his Rasool. Allah is All-Knowledgeable, All-Wise.