Banks are literally the cornerstone of the economy. I'm not aware of any restaurants of convenience stores that are even close to being as critical or 'too big to fail.'
Banks aren't too big to fail just because they are banks. If they weren't allowed to get so big or merge together, they they wouldn't be too big to fail.
They're too big to fail because politicians decided they were. Of course, they aren't actually too big to fail. In the financial crisis, if they hadn't bailed out the banks, they'd either be acquired by competitors, or go out of business and people would have actually learned their lessons to not take on excessively risky assets. Instead, the government bailed out the banks, essentially telling them that they should take on whatever risk they want, because they'll just be bailed out whenever they fail.
