It appears to me that they could not even wait until the end of March to retire them as planned.
How do you come to that conclusion?
They are still flying this week, so those aircrew are now current until beyond 31 March. There comes a point when no more routine flying is needed to sustain the required capability until the end of the funded period. My understanding is that the aircraft remain ‘on the hook’ for operations until the end of March; they just don’t need to fly them routinely for much longer. That is sensible risk management.