The answer to 'why is my sod mud' is that your newly laid sod is likely saturated with water, causing it to become muddy and unstable. This can happen due to overwatering, poor drainage, or heavy rainfall shortly after installation.
Sod needs consistent moisture to establish its roots, but too much water can lead to the soil becoming waterlogged and the grass becoming muddy. This can be a common issue, especially in areas with clay-heavy soil or low spots in the yard that don't drain properly.