Bank of America's assets total over 2 trillion dollars. I would imagine it's easier for large financial institutions to create such strong guarantees for its users.
Marc came to our office at midnight and read the letter I’d written to our community about the Airbnb Guarantee, and the two changes he made changed the company forever. I’d said we guarantee five thousand dollars for property damage, and he added a zero, which seemed crazy.”
That's kind of the point - if you have large assets, that might be some assurance of your liquidity if e.g. a $100 million bad event happens; but if you do not and can't pledge large amounts of capital as pretty much a collateral, then you'd be expected or even required to buy insurance for very large amounts.
-- http://www.newyorker.com/magazine/2015/05/18/tomorrows-advan...