It is pretty predictable that they would experience a bank run given interest rates going up though. They locked the money up for way too long so it would've impacted the interest rates they could offer, meaning people would want to move their money outside of any panic instinct. Maybe if it were a bit more spread out over time they wouldn't have entirely collapsed, but they put 40% of their deposits in these things, it still definitely would've stung.
Not disagreeing that MBS is irrelevant, and yeah the risk rating of the bond wasn't a problem as this will pay what it said is would. Just saying it was a stupid move to buy such a large amount of such a long term bond when interest rates can't go anywhere but up and you're using borrowed money to do it. From that perspective it was a risky move.
It was stupid to not hedge that interest rate risk. I mean, the Fed telegraphed their moves well in advance. I don't work in finance but it doesn't take a genius to see how that dynamic would play out if that's your job. Not something I would've thought about till now but if banking is your business, you tend to think of ways it can break and this seems as elementary as anything if your job is to ensure solvency in all conditions. I just hope other banks weren't this stupid.
The problem in 2008 wasn't really MBS it was the way they were packaged.
You take a collection of n mortgages and rank them by how likely they are to default, and then you divide them up into say 5 different securities each containing n/5 mortgages. The top 20% will be considered the least risky and the bottom 20% the most risky, and yields will reflect that. There are also rules on what risk level different asset managers are allowed to take on, so random retirement accounts wouldn't take the bottom 20%. No problem yet.
But then some "spherical cow" style math was applied to these things. If mortgage defaults are independent events then mathematically you can smooth out the risk even from the high risk ones by just grouping a bigger number together. So they took say 5 different shit tier mortgage collections, lumped those mortgages together to create another pool of size n, and repeated the process. Now the top 20% of that pool was given a very low risk rating, yet it still paid a greater yield than the original pool's top 20%, so why wouldn't an investor want to get in on this high yield safely rated security?
And it didn't stop from there, the bottom say 20% of those pools were again pooled together to create more supposedly safer securities.
This could've held up for a long time in a vacuum, as long as mortgage default rates didn't change too much. But part of what incentivized this system in the first place (and in turn what this system incentivized) was to hand out mortgages like candy basically.
So it was a house of cards waiting to fall, and once some of these securities faltered it also caused a bank run on a wider set of MBS structures that probably could've held out if not for the panic. Plus big failures like Lehman Brothers and Bear Stearns had impacts on firms that went beyond MBS activity, so there were some crazy cascade effects too.
Anyway, there's nothing inherently wrong with MBS, it's just important to know what you're buying. This situation is weird because it's not that the security itself is unsafe, it's the context in which they are using it that is risky. Though I suppose it relates on the high level that they probably thought "this security is rated very safe and it gives relatively high yield" without an actual understanding of the risk involved in their use case.
