The answer to 'why is my patio disease' is that your patio may be suffering from a variety of issues, including mold, mildew, or other fungal growth. These problems can be caused by poor drainage, excessive moisture, or lack of sunlight exposure.
Some common symptoms of patio disease include discoloration, slippery surfaces, and the presence of green or black growth. To address these issues, you may need to improve drainage, increase air circulation, and regularly clean and maintain your patio. In some cases, you may need to call a professional landscaper to assess and treat the problem.