Because the poles are where the ozone layer is the thinnest, due to the rotation of the Earth

This is just a guess, based on the fact that Earth is not a perfect sphere; it bulges in the middle ever so slightly.

Also, when CFCs are released, they don't necessarily go straight up. Being in gaseous form, they disperse all over the atmosphere until they find their way to the ozone layer, then nibble away at it.

And since it is being depleted uniformly, the thinnest part is the first to go. Like hair on a bald spot.

Introduction:
The ozone layer is a protective layer of ozone gas in the Earth's stratosphere that shields us from harmful ultraviolet (UV) radiation emitted by the sun. However, the ozone layer has been depleting due to the release of certain chemicals called ozone-depleting substances (ODS), such as chlorofluorocarbons (CFCs) and halons. While ozone depletion occurs globally, it is more pronounced in cold regions.

1. Temperature:
The temperature in cold regions is significantly lower compared to warmer regions. This cold temperature plays a crucial role in the ozone layer loss. The reactions responsible for ozone depletion are highly temperature-dependent, and colder temperatures enhance these reactions.

2. Polar Stratospheric Clouds (PSCs):
In cold regions, especially near the poles, the stratosphere becomes very cold during winter. This extreme cold leads to the formation of Polar Stratospheric Clouds (PSCs). PSCs provide a surface for chemical reactions that break down ozone. The presence of these clouds enhances the efficiency of ozone depletion processes, resulting in a higher rate of ozone loss.

3. Ozone Destruction Reactions:
The primary mechanism responsible for ozone depletion involves chemical reactions with chlorine and bromine. In cold regions, these reactions occur more frequently due to the presence of PSCs and lower temperatures. Cold temperatures slow down the recombination reactions that regenerate chlorine and bromine compounds, allowing them to persist longer and continue destroying ozone.

4. Polar Vortex:
During winter, cold air is trapped in a circulation pattern known as the polar vortex. This vortex isolates the polar regions from the rest of the atmosphere, creating a stagnant air mass. As a result, ODS released in these regions are confined within the vortex, leading to higher concentrations of ozone-depleting substances and accelerating ozone destruction.

Conclusion:
In conclusion, the loss of ozone layer is more significant in cold regions due to a combination of factors. The low temperatures enhance the efficiency of ozone destruction reactions, while the presence of PSCs provides a surface for these reactions to occur. Additionally, the polar vortex traps ozone-depleting substances, leading to higher concentrations and increased ozone depletion. Understanding these factors is crucial for devising effective strategies to mitigate ozone layer depletion and protect the Earth from harmful UV radiation.