I'm not knowledgeable at all about this, but from what I've read the SVB investments weren't bad. Those will still pay out eventually, correct?
Here's a super-simplified version: The bank took in a bunch of money from people depositing. They needed to put that money somewhere safe that earned some kind of return, and there's nothing better, safer, or more reliable that US government bonds. Unfortunately, at the time, bonds paid like 1.5% interest... for every $100 they bought, they'd get back $101.50... but over time, yes, those will still pay out at a profit. But, when you buy bonds, you lock up the money for like 20 years.
The way around that timeframe, of course, is the bond market, where if you need to get out of a bond before the 20 years are up, you can sell it to someone else. So when the people who deposited suddenly wanted their money back all at once, the bank would go to the bond market and try to sell the bonds.
But, now that interest rates have gone up recently, you can buy bonds direct from the government that pay, like, 4%. So all the buyers out there would look at SVB's bonds and ask "why would I buy a 1.5% bond from you when I can buy a 4% bond from Uncle Sam?" The only thing SVB could do, then was to sell their bond at a loss. That is, they'd sell their $100 bond which paid out $101.50 to a buyer for only $97. That way, the buyer was getting a favorable return... for him, he's paying $97 for $101.50, and getting about 4% return on his money, same as he would get from Uncle Sam. That discount makes it possible for SVB to sell at all.
But for SVB, that means they're losing 3% of their depositors money. Coming up 3% short on their customers is what makes a bank fail... no one is going to stay with them.