The answer to 'why is my retaining wall' is that there are several common causes for issues with a retaining wall, including improper construction, soil erosion, poor drainage, and natural settling over time. Symptoms may include cracks, leaning, or bulging in the wall, as well as water pooling behind it.
To address these problems, the first step is to identify the underlying cause. This may require an inspection by a professional landscaper or structural engineer. If the wall was not properly built, it may need to be reconstructed. Drainage issues can often be resolved by installing or improving the wall's drainage system. In some cases, the wall may need to be reinforced or anchored to prevent further movement.