Here's why:

* Sedimentation: The central Pacific basin is far from continental landmasses, meaning there's less input of terrestrial sediment. This allows for thick accumulations of pelagic sediments (formed from the remains of marine organisms) to build up over the igneous rocks of the ocean floor.

* Tectonic Setting: The central Pacific is dominated by the Pacific Plate, a massive oceanic plate. This plate is relatively old and has been moving for a long time, allowing for more time for sediment accumulation.

* Mid-Ocean Ridges: The North Atlantic basin has a more active mid-ocean ridge system than the central Pacific. This means there's more volcanic activity and associated rough topography, which limits the extent of smooth abyssal plains.

Therefore, the abyssal plains in the central Pacific basin are generally more extensive and covered by thicker layers of sediment compared to those in the North Atlantic.