They bought a bunch of long dated stuff. The credit quality isn't the problem here, it's the sensitivity to interest rates rising. The value of those long dated bonds fell by $15 billion - almost equal to their total equity capital. It was 40% of their assets. On top of that, they had flighty deposits - not grandma with her $100k in the bank which is FDIC insured, startups with millions in the bank who knew they weren't insured. It was incredibly stupid to be so heavily weighted in long term bonds. As dumb as it gets in banking.

All major banks don't have the same problem. The vast majority of them had/have a portfolio of assets with a weighted average duration significantly shorter than SVB because they understood there was a risk of interest rates rising significantly from the extremely low levels they were at. And most banks have stickier deposits than SVB. So - all banks lost money on their long dated assets, but not the same % of their equity capital (because it's a lower % of their assets) and not with depositors who are likely to pull money fast.