"Dirty" means not clean or pure, and it can be used to describe a variety of things, including physical objects, surfaces, or even people. There are many possible reasons why something might be dirty, including exposure to dirt, grime, or other contaminants, lack of proper cleaning or maintenance, or simply being used or handled without care.

Here are some possible Engpsh phrases that might be used to describe the reason something is dirty:

"It's dirty because it hasn't been cleaned in a while." (This might be used to describe a surface or object that has accumulated dirt or grime over time.)
"It's dirty because it was used to do something dirty." (This might be used to describe something that was used in a way that caused it to become dirty, such as a tool that was used to dig in the dirt.)
"It's dirty because it was handled without care." (This might be used to describe something that has become dirty because it was not handled carefully or properly, such as food that was dropped on the floor or clothes that were not washed after being worn.)

Here are some examples of these phrases in context:

Example 1:

Person 1: "Why is this kitchen counter so dirty?"
Person 2: "It's dirty because it hasn't been cleaned in a while. I'll wipe it down now."

Example 2:

Person 1: "Why is this shirt so dirty?"
Person 2: "It's dirty because it was used to do something dirty. I was using it to paint the bedroom."

Example 3:

Person 1: "Why is this plate so dirty?"
Person 2: "It's dirty because it was handled without care. Someone just left it on the table after eating, and now there's food all over it."