The answer to 'why is my bathtub slow draining' is a clogged drain. Slow draining in a bathtub is typically caused by a buildup of hair, soap scum, and other debris in the drain pipe. This can restrict the flow of water and cause it to drain slowly.
Some common symptoms of a slow draining bathtub include water taking a long time to drain, the tub filling up during a shower, or a gurgling sound coming from the drain. To fix this, you'll need to clear the clog from the drain pipe.