Second, the market didn't just crash in 2008, it melted down. There were fears of simultaneous runs on global banks with catastrophic consequences. Bernanke/Geithner/Paulson orchestrated government backstops on money market funds, on Fannie/Freddie debt, on shotgun-marriages between banks, on defusing the credit default swap nightmare constructed by AIG and its counter parties. ZIRP and QE were brought in to juice spirits in the hopes of rescuing growth.
2008-2009 was the end of the financial world as we knew it going back to Paul Volcker. It was nightmare. It was a catastrophic end that many and been predicting for some time. Some saw the writing on the wall by 2005 and were positioning their investments accordingly. Read about the thoughts of Ray Dalio, Stan Druckenmiller, or Jeremy Grantham.
Since 2008-2009, we're now in a whole new regime. Perpetual QE + ZIRP is not in ur economic textbooks and I do not believe our models can tell us what is coming.
We had an opportunity when things were stable in 2010 to find a sustainable path forward. Instead, worldwide, we've just taken regular hits of QE.