A desktop rarely shows the wallpaper straight any more. Windows pulls a tint out of it for the title bars, macOS floats sidebars and menus on a translucent layer, and both blur whatever sits underneath with a radius wide enough to erase anything smaller than a leaf. What reaches you through a panel is not the photo but its local average.
That average is hard on busy pictures. A forest floor with a thousand small contrasts flattens into olive grey, gravel turns to wet cement, a skyline loses the lit windows that made it a skyline. Broad shapes survive, because blur only removes the frequencies that were fine to begin with: one soft light source, a wall out of focus, a sky that changes slowly from top to bottom.
Then there is the text sitting on top. Panels are drawn at a fixed opacity, so a bright patch of sky under a sidebar lifts the whole panel and the small grey labels go first, while the same panel over a dark corner stays readable. Choosing a wallpaper for a translucent desktop is mostly choosing where its bright areas land, and the safe place is the middle, where windows are not.
