If these big banks are so confident in First Republic not failing, why not just purchase First Republic stock (or acquire it outright for its current market cap

If these big banks are so confident in First Republic not failing, why not just purchase First Republic stock (or acquire it outright for its current market cap of $5b)? My hypothesis is that they don't actually believe in First Republic. They just want the contagion to not spread. And, sending uninsured deposits is actually the least risky way to do that since deposits are at the very top of the liquidation stack.