EDIT: To be clear, think of it this way. I have a piece of paper saying you'll give me $100 in 1 year plus 1% interest that I bought for $98.
No-one buys that piece of paper for $98 today, because they can get the same deal with better interest. But that doesn't change the fact that I will get $100 for it.
If deposits hadn't shrunk, $100 would go to SVB in 1 year and everything would be fine, it's the fact that they have to sell it so far ahead of maturity that's the problem, we just didn't notice this phenomenon in the past few decades b/c rates fell and prices went up.
This is not because SVB has a particularly risky book (we're talking treasuries here), it's because they didn't account for declining deposits (itself a very stupid, but unique bad decision unrelated to their risk tolerance).