The answer to 'why is my paver brown patches' is that the most common cause is a buildup of dirt, debris, and organic matter in the paver joints. This can lead to unsightly brown or discolored patches on the surface of your pavers.
Some other possible causes include water stains, mold or mildew growth, or chemical reactions between the pavers and the soil. These issues can be exacerbated by poor drainage, lack of maintenance, or exposure to the elements over time.