I'm gonna seem like a genius or put my foot in my mouth here but here is my take on this....
The FED purchases were just "liquidity injections" and the MBS/ABS were just the easiest way to inject that cash. It's essentially a cash infusion to mitigate an unexpected increase in regulatory required reserves. (credit crunch froze up credit markets, this would have caused serious problems for entities who need to refinance continually)
The banks are constantly rolling over debt portfolios and extending credit to counter-parties that need to do the same.
Also Fannie, Freddie, Ginnie, FHA, VA and the rest were gonna be called on for mortgage default risk in orders of magnitude above what was anticipated. Markets were in free fall....
The FED became "the lender of last resort" when the shit hit the fan vis a vis indexed credit derivatives........these are instruments that allow institutions to make markets on credit instruments (CDO, CDS, MBS,ABS, CLO)
This is all about regulated reserve requirements for US bank chartered institutions.
Re the REPO rate. I'm def not the guy to do this analysis, but here goes....
Read this article
https://www.wsj.com/articles/how-the-discount-window-became-a-pain-in-the-repo-market-11574337601
"Banks have all but abandoned the Federal Reserve’s discount window...."
and
"[cash] hoarding has drained liquidity from other parts of the market, contributing to a cash shortfall that roiled overnight-lending markets..."
I don't know enough about the intricacies of bank financing to really say more than the WSJ.
One thing you have to remember is that these banks (Morgan, Goldman, Citi, etc.) are trying to beat each other on earnings. They are pushing the envelope in terms of total invested funds (non reserve activity). This means less free cash to meet reserves, and so they will basically just keep money and not lend it via repo market.
Also remember that the repo market is not small. They do single orders in the hundreds of millions to billions. If the whole banking system starts to lean on this then things could get out of hand LOL.
When Bear went under they needed billions in immediate cash and they couldn't get it because the street knew they were going under. I'd say this is not the case today.
This is a story about the too big to fail banks needing more liquidity because they are getting aggressive in the markets.
Look at these levels in global markets. It takes cash get the S&P to 3250! Global markets are sucking up cash, and risks have to be hedged.
I think you are right in your analysis. But when does anyone cash out? Is S&P the new overnight repo?
One thing for sure is I'm going to start scripting a download of the fed balance sheet. Not because it will make any difference to me but because it will help me understand the past. And I want to catch these basterds when they change something without announcing it.