The answer to 'why is my shower constantly running' is that the most common cause is a problem with the shower valve or faucet. This could be due to a worn washer, a faulty cartridge, or a problem with the internal components of the shower valve. The constant running can be caused by a valve that is not fully closing or a faucet that is not sealing properly.
If your shower is constantly running, you'll likely notice that water is continuously flowing from the showerhead, even when the shower is turned off. This can waste a significant amount of water and drive up your utility bills. In some cases, the constant running may also cause water damage to the surrounding areas if the leak is not addressed.