Climatic modelling has been unable to justify the currently lower amounts of ozone to purely natural occurrences. Thus there must be other contributions. Free radical chlorine atoms catalytically breakdown ozone by reacting with it to form a more stable oxygen product. Thus the ozone is being destroyed, while the chlorine free radicals are free to keep on reacting. Because it is so cold, that water freezes in the atmosphere and the ice crystals provide a surface on which the ozone depleting reactions can occur, speeding the breakdown process.
Governmental response is mostly political.