Unlike soft materials like snow or papier mache, there's no clumping or bumps, unless you want them. Unlike stone, you don't need heavy tools. Plastic media, such as clay, have minds of their own in that they take on lumps and surface textures that are hard to change. They're also floppy. Sand stays where you put it and takes the surface you put on.
Sand ranges from flour fineness to near pebbles, pure one color to polychrome, white to black.
Some grains are angular, some are rounded. The grains' sizes can be uniform or variegated. All of it will make piles. If the grains are angular, they stay even better, and added clay helps even more. Ocean beaches tend to be monocultures, while lake beaches have a range of grain sizes from silt on up.