Why is this happening now?
Over the past 18 months, interest rates have gone up quite a bit. This means it is more expensive to take on debt, whether this is for investment or consumption purposes. When debt is more expensive economic activity slows. Additionally, inflation has gone through the roof which implies people can buy less with the same resources. Again, this has a negative effect on economic activity.
When economic activity slows, accumulated savings dry up and people that were not withdrawing money from their bank deposits now need to. This is the first component of the above-described banking system. The other is related to, for simplicity purposes, mortgages. When economic activity slows, people lose their jobs and they cannot pay their mortgages. As a consequence, banks have it even harder to liquidate their long-term assets to meet higher withdrawal demand.
Pair this with the artificially high withdrawal demand caused by panic and lack of trust on a banking institution, and you have what is commonly known as a bank run: everyone wants their deposits back and the bank does not have enough liquidity to meet demand and is forced into liquidation.
Finally, technology allows for withdrawals at a much higher speed than in the past. As a “fun” fact (this really sounds terrible in this context), the previous largest bank run in modern banking history took place at Washington Mutual bank in 2008. People withdrew $16 billion over the course of 10 days. Last week, customers withdrew $42 billion from SVB accounts in 1 day!