The answer to 'why is my drain trap burst pipe' is that a burst or cracked drain trap is usually caused by freezing temperatures, physical damage, or a buildup of pressure. Symptoms include water leaking from the trap, slow draining, and foul odors. To fix a burst drain trap, you'll need to replace the damaged trap, which may require calling a professional plumber.
Drain traps are the curved section of pipe under a sink or floor drain that holds water to prevent sewer gases from entering your home. If the trap freezes, the expanding ice can cause the pipe to crack or burst. Traps can also become damaged over time from corrosion or physical impact. And in some cases, a blockage in the drain line can build up pressure and cause the trap to rupture.