Because a lot of stuff died there in pre history times and they have very relaxed rules about getting access to it.

Also because it is so easily accessible. Here in North America we have to pump oil out of the ground….slowly. In the gulf, if a well was such low production they have to pump it, they would shut it down. They can just dig a hole and it pushes itself out of the ground, at high rates.

Oil and gas form from organic material such as marine zooplankton and phytoplankton, originally concentrated in shales, mud-rich limestones and other rocks exposed to elevated temperatures and pressures. When rocks are composed of at least 2% organic material, they are considered to be high quality for oil and gas generation.

The Gulf region has a particularly large number of layers of such source rocks, some of which are especially thick, widespread and organically rich. Examples are the Hanifa and Tuwaiq mountain formations on the Arabian side of the Gulf, which formed during the Jurassic period, about 200 million to 145 million years ago, and the Kazhdumi formation in Iran, which formed in the Cretaceous period, about 145 to 66 million years ago. These rocks have between 1% and 13% organic content, and even more in some places.