The answer to 'why is my drainage system bare spots' is that there are several common causes, including clogged drains, improper grading, and damage to the drainage pipes. These issues can lead to standing water, erosion, and bare patches in the landscape.
Clogged drains can prevent water from flowing properly, causing it to pool and kill the grass. Improper grading, where the ground slopes towards the home instead of away, can also lead to drainage problems and bare spots. Damage to the drainage pipes, such as cracks or breaks, can allow water to seep out and erode the soil.