The answer to your question is easy. If you don't use it, you lose it.
Humans evolved to eat meat with fat, and when you go on a low fat vegan or vegetarian diet, your gall bladder is no longer used enough to stay healthy, and it starts filling up with sludge. The sludge eventually turns into gallstones.
It is tough for vegetarians to switch over to a Paleo diet, which requires eating fat & meat. The answer is to SLOOOWLY transition the gallbladder back to good health by titrating coconut oil into meals over many months.
Sorry, but no one is going to spend $$millions to scientifically prove this FACT that is common sense, and no one is going to spend $$millions to prove that a $25 liver detox works. The Medical Profession will not discuss Gallbladders. Doctors will just surgically remove your gallbladder without a second thought. There are methods of breaking up the gallstones using intense sound waves, but it is hard to find any doctors willing to do this. All the MONEY is made in surgeries, and that is what doctors will insist you to do. Save your gallbladder? The doctors will laugh at you. They want your MONEY for surgery and they want that hospital bed filled. They can't buy that vacation home by saving your Gallbladder.