The answer to 'why is my downspouts missing shingles' is that the downspout is likely causing water damage to the shingles around it. Downspouts that are not properly secured or positioned can direct water flow onto the roof, eroding the shingles over time. This can cause the shingles to become loose and eventually fall off.
The solution is to ensure the downspout is securely attached, properly angled, and directing water away from the roof. This may require adjusting the downspout's position or adding additional support brackets. If the damage is extensive, you may need to replace the affected shingles to prevent further leaks and water damage.