Interesting here is the connotation of ‘flattening’ or dimensional reduction…

explain (v.)

early 15c., from Latin explanare “to explain, make clear, make plain,” literally “make level, flatten,” from ex “out” (see ex-) + planus “flat” (from PIE root *pele- (2) “flat; to spread”).

Originally explane, the spelling was altered by influence of plain. Also see plane (v.2). In 17c., occasionally used more literally, of the unfolding of material things: Evelyn has buds that “explain into leaves” [“Sylva, or, A discourse of forest-trees, and the propagation of timber in His Majesties dominions,” 1664]. Related: Explained; explaining; explains. To explain (something) away is from 1709.