why is the gallbladder located under the liver in pig?

Its in the same place in all mammals.  

Everything gotta be someplace.

Because pigs descended from a remote ancestral mammal in which the gallbladder was under the liver.

As far as I know that is where it is in all mammals, including us humans. Bile is constantly produced in the liver and secreted by it. Bile gets stored in the gallbladder so near the liver is a convenient place. The gallbladder releases bile when stimulated to do so by the presence of lipids in the duodenum. That is what bladders do, they are storage reservoirs.

Where the hell else should it be?

cause thats where god put it

Same as in most mammals

because gall (which anglos call "bile" for some reason) is produced by the liver, and stored in the gallbladder so it can be released into the small intestine when needed

It is in humans too. It is because the liver secretes bile into the gall bladder to store for digestive use when the stomach is digesting fats.