Uxbridge branch suspension

Just come arrived home and as I was leaving the tube there were announcements about the Piccadilly and Met lines being suspended up the Uxbridge end due to a shortage of staff.  I had a look on the Picc's Twitter feed to see if there was any more info, and I saw Arsenal station was shut earlier because of a lack of staff!

How does this happen? Suggests some really poor planning from management, and just plays into the hands of those arguing for less staff at stations if they can't be relied upon to keep the lines running!  If threads on the board are anything to go by, recruitment for TfL shouldn't be a problem - are they trying to run it as close to the line as possible to save on costs?

Accidents and sickness can occur without advance warning and management may not have enough time to get somebody else in place for the planned start of shift.