Why does "organic" milk have a shelf life like 4 times longer than regular milk?

It’s probably Ultra-Pasteurized, which gives it a longer shelf life. I buy Heavy Cream from an organic dairy that does this.

From the Topeka Capital-Journal

But many organic milk companies employ a process known as ultrapasteurization (indicated on package) in which milk is heated at a higher temperature until it is practically free of organisms that can grow at refrigeration temperatures; this allows it to last one to two months instead of the 10 to 12 days you may be accustomed to.

However, it is important to note that the sell-by date on ultrapasteurized products is relevant only before you open the carton. After that, the milk stays fresh for a week or so.

Ultrapasteurization isn’t used only for organic milk, but it is particularly advantageous for this product. An extended expiration date enables organic dairies to ship their products farther and allows stores to receive shipments less often.