Here's why:

* Abyssal plains are vast, flat areas of the deep ocean floor. They are the flattest regions on Earth.

* Sedimentation is the process of sediments, such as sand, silt, and clay, settling to the bottom of the ocean.

* Over millions of years, these sediments accumulate in thick layers, burying any irregularities in the ocean floor, creating the flat, smooth surface of abyssal plains.

Let me know if you have any other questions!