I'm not very financially literate. How does SVB shareholders getting nothing translate to shareholders of all other banks being in the same situation?
If the same thing happens to other banks - everyone withdraws, they shut down and the government steps in - the assumption is that their equity will eventually be worth $0 too. So, everyone sells at >$0.
It's not going to be all banks, though.
And there was a bank run because the investors panicked and caused the share price to plummet. Depositors saw stock plummeting, got nervous and pulled out. If this type of thing spreads to other banks we'll have a bad time.
It also simultaneously stepped in to preemptively save similarly-situated [0] banks, though.
[0] to the condition SVB was in which led ultimately to the bank run.