The answer to 'why is my drain trap clogged' is that the drain trap, the U-shaped pipe under your sink, has likely become blocked with debris, hair, or other materials. This prevents proper drainage and can cause water to back up in your sink.
Some common causes of a clogged drain trap include buildup of soap scum, food particles, hair, and other debris that gets washed down the drain. Over time, this can accumulate and restrict the flow of water, leading to a clogged drain trap.