What are reasons why would the removal of the gall bladder cause diarrhea?

It doesn't. Removing the gallbladder does not lead to diarrhea , as your bile production has not changed. Some people do develop urgency after gallbladder surgery. That is, about 30-40 minutes after eating the patient has an aggressive need to have bowel movement which may be loose. This is self limited, but can be eliminated with Imodium (loperamide) ad. I allow my patients full dietary intake after surgery. Good luck.