The answer to 'why is my P-trap' is that a clogged or malfunctioning P-trap is a common plumbing issue that can cause water to back up or leak under your sink. The P-trap is the curved pipe underneath your sink that is designed to hold a small amount of water, creating a seal that prevents sewer gases from entering your home.
Some common causes of a problem with the P-trap include a blockage from debris, a broken or dried-out seal, or improper installation. Symptoms may include water leaking from under the sink, a foul odor coming from the drain, or water not draining properly. Solutions can range from a simple DIY unclogging to replacing the entire P-trap, depending on the severity of the issue.