The answer to 'why is my roof vent missing shingles' is that it's likely due to deterioration or improper installation of the roof vent. Over time, the sealant and shingles around the vent can become worn, cracked, or come loose, causing the shingles to go missing. This can happen due to weather exposure, poor installation, or the natural aging of the roofing materials.
If the missing shingles are limited to just the area around the roof vent, it's usually a localized issue that can be fixed without replacing the entire roof. However, it's important to address the problem promptly to prevent further damage and leaks.