Partly as a result of this, the monetary response has needed to be larger. This line of argument recognises the considerable damage caused by the financial crisis, but sees economic activity and inflation responding in only a relatively muted way to the monetary stimulus, with central banks having to do more to achieve their mandated goals.
There is probably an element of truth in both of these answers. The shock caused by the financial crisis was indeed a very large one and a very large monetary response was appropriate and helpful. At the same time, though, the transmission of the monetary stimulus does look to have been a little different through this episode.