Banks have a ton of cash, and they're worried about inflation. So, they store their cash with the fed (through a repo [repurchase] agreement) temporarily.
The immediate situation is a problem of money market funds having more inflows than they could allocate (without nominal losses) in a zero interest rate environment. It's not about inflation per se.
If inflation happens, the 30-year bond will likely rise with inflation: maybe 3% or 4%. It is better to store your cash today, than to "lock in" to 2.2% APY.
Next month, if inflation starts to kick in, maybe you'll get 3% over the next 30 years instead of 2.2% over the next 30 years.
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Obviously, a 30-year bond is 'different' than cash. However, when you start looking at 6-months, 3-months, 1-month, and overnight lending rates... things look more-and-more like cash.
No one ever holds "cash" per se, its always better to lend it out (even for only 1 day, you wanna have that cash generate more cash). By betting on shorter timescales (ex: 1-month), you're really betting that the longer-time scale bonds (ex: a 30-year) will rise up.
Contrary to the other two replies, yes, they are paid interest (it's a reverse of the standard repo where they borrow money from the Fed and pay the interest)
Banks don't like holding cash (because it doesn't belong to them, and could be withdrawn at any time). So it's actually the opposite: they pay for the privilege of not having to hold onto that cash.