I think why Shedd is so successful is they have a lot of pledges and have more members than any public institution in Chicago(an impress feat considering all the amazing public institutions there.)
But Shedd came about because of their World Fair, St. Louis had a world fair that STL Zoo was pretty much established on. Yet no aquarium. The aquarium exhibit was just dumped. St. Louis had more people and more money than Chicago back in 1904. It could have been done! But while Shedd is an older aquarium that has grown, Georgia Aquarium(largest in America) is new! Why did Atlanta get it? They had a really rich guy(Home Depot tycoon) give $250m and then some other companies donated some millions. STL- we need to find our really rich person to fund our aquarium. =( There are a lot of companies headquartered in STL, surely someone is out there who is good for the money. Surely?
Wanted: Really rich person to fund STL Aquarium