Why are sedimentary rocks found as a veneer (thin layering) that covers large areas of the continental and oceanic igneous rocks?

The sedimentary rock cover of the continents of the Earth's crust is extensive (73% of the Earth's current land surface[1]), but sedimentary rock is estimated to be only 8% of the volume of the crust.[2] Sedimentary rocks are only a thin veneer over a crust consisting mainly of igneous and metamorphic rocks. Sedimentary rocks are deposited in layers as strata, forming a structure called bedding. Sedimentary rocks are often deposited in large structures called sedimentary basins. Sedimentary rocks have also been found on Mars.

The study of sedimentary rocks and rock strata provides information about the subsurface that is useful for civil engineering, for example in the construction of roads, houses, tunnels, canals or other structures. Sedimentary rocks are also important sources of natural resources including coal, fossil fuels, drinking water and ores.

the dependant variable is spilled water

the independent is the heat

if you're asking what comes out, it's steam.