At its simplest, depositors need to trust that when they put their money into a bank they have certainty of being able to withdraw that money in the future. Similarly, banks need to trust that when they gather these deposits, and lend at longer maturities, they will either be repaid, or in extremis be able to enforce collateral.
Secondly, in an environment of heightened financial market uncertainty actual monetary dynamics may to a large part be driven by noise which does not necessitate a monetary policy reaction. The portfolio-shift adjustment of money growth in the post 2001 period can be seen as an example.