The answer to 'why is my pressure regulator' is that the pressure regulator may be malfunctioning or set to the wrong pressure. A pressure regulator is a device installed on the main water supply line to your home that controls the water pressure entering your plumbing system. If it is not working properly, it can lead to issues like low water pressure, water hammer, or even damage to your pipes and appliances.
Some common causes of pressure regulator problems include wear and tear over time, debris or mineral buildup, a faulty regulator, or the regulator being set to the wrong pressure. Symptoms may include low water pressure, fluctuating pressure, or water hammer (banging pipes). To fix the issue, you may need to adjust, repair, or replace the pressure regulator. This is a task that is generally best handled by a professional plumber, as they have the right tools and expertise to properly diagnose and fix the problem.