The answer to 'why is my drip edge missing shingles' is that the drip edge may have come loose or been damaged, causing the shingles to detach from the edge. This can happen over time due to weather, age, or improper installation. The missing shingles can allow water to seep behind the roofing and cause leaks and damage.
To fix this issue, you'll need to inspect the drip edge and replace any missing or damaged sections. This may require removing and reinstalling the affected shingles. If the problem is widespread or you're not comfortable working on the roof, it's best to call a professional roofing contractor to assess and repair the issue.