Publicly traded companies are never governed by the majority of shareholders, they are governed by the shareholders with a majority of shares. And those folks don't have the same interests as you do.
Companies are governed by their share price. If the government repealed too big to fail the share price of large banks would fall, which would cause those companies to break themselves into more manageable pieces. Even Microsoft will be forced by its investors to change it ways if it does not start earning Apple sized money soon.