The answer to 'why is my sod' is that there are several common reasons why sod may be struggling, including improper installation, lack of water, poor soil conditions, or pest/disease issues. Symptoms can include discoloration, thinning, or patchy growth.
To troubleshoot, first check that the sod was installed correctly with proper soil preparation and that it is receiving adequate water, typically 1-2 inches per week. If the soil is poor, amend it with compost or topsoil. Inspect for signs of pests or disease and treat accordingly. If the issues persist, it's best to consult a professional landscaper who can diagnose and resolve the problem.