The answer to 'why is my shrub drainage problems' is poor soil drainage or overwatering. Shrubs require well-draining soil to thrive, and if the soil around the shrub stays saturated, it can lead to root rot, wilting, and other issues. Symptoms of poor drainage include yellowing or wilting leaves, fungal growth, and standing water around the base of the plant.
To address shrub drainage problems, you can try improving the soil by adding compost or sand to increase drainage, installing a French drain or other drainage system, or adjusting your watering schedule. If the problem persists, it's best to consult a professional landscaper who can assess the issue and recommend the appropriate solution.