Why is there very little evidence or motte and bailey castles?

There is very little evidence of motte and bailey castles primarily due to their construction materials and the passage of time. Many of these structures were built using wood and earth, which are less durable and have eroded or decayed over the centuries. Additionally, many motte and bailey sites have been repurposed or built over, making archaeological investigation challenging. Consequently, the surviving remnants are often minimal, leading to a limited understanding of their original design and function.