The answer to 'why is my skylight' is that there could be several common causes for issues with a skylight, including leaks, condensation, or damage. Skylights can develop problems over time due to wear and tear, improper installation, or exposure to the elements.
Some common symptoms of skylight issues include water stains on the ceiling, mold or mildew growth, drafts, or the skylight itself appearing cracked or damaged. Solutions can range from simple DIY repairs like re-caulking or replacing weatherstripping, to more complex issues that may require a professional roofer to inspect and fix, such as replacing the skylight entirely.