We had a solution to "too big to fail" for banks. There was the Glass-Steagall Act, which forced a complete separation between brokerage and banking. Worked fine from the 1930s to 1999. Then it was repealed because the big banks wanted to get bigger. "Today, Congress voted to update the rules that have governed financial services since the Great Depression and replace them with a system for the 21st century. This historic legislation will better enable American companies to compete in the new economy.", said the Treasury secretary in 1999.
Right there is how we got into this mess.