As long as the tap adds water as fast as the drain removes water, the water level in the tub remains constant. Similarly, while ozone production and destruction are balanced, ozone levels remain stable. This was the situation until the past several decades. Large increases in stratospheric chlorine and bromine have upset that balance. In effect, they have added another drain to the tub, removing ozone faster than natural ozone is created.
Winds efficiently mix the troposphere and evenly distribute the gases.
CFC's are extremely stable, and they do not dissolve in rain. After a period of a few years, ODS molecules reach the stratosphere. Strong UV light breaks apart the ODS molecule. CFC's release chlorine atoms and halons release bromine atoms. It is these atoms that actually destroy ozone, not the intact ODS molecule.