The question "Why do they do this?" expresses a desire to understand the reasons or motivations behind a specific action or behavior, often in response to something surprising, disappointing, or confusing. While it could be a simple query for cause or motive, it often implies a lack of understanding or even a feeling of betrayal on the part of the questioner.

Here's a breakdown of what "Why do they do this?" can imply:

A Question of Cause:

The phrase seeks to understand the immediate triggers or circumstances that led to the action.

A Question of Motive:

It can also ask about the underlying purpose or goal the person hopes to achieve through their action.

An Expression of Disappointment or Betrayal:

In some contexts, particularly when the action is perceived as negative or harmful, "Why do they do this?" conveys disappointment or a feeling that trust has been broken.

A Cry for Certainty:

On a deeper level, people often seek to understand the actions of others to reduce uncertainty and find a sense of predictability or comfort in their lives.

An Interjection of Surprise:

The phrase can also function as an interjection, expressing shock or disbelief at an unexpected event.