Why can't we take a single photograph of the Milky Way's entire structure?

We are physically trapped inside of it.

The fundamental limitation preventing the creation of a true, unified snapshot of the Milky Way galaxy stems from our observational position. Because the Solar System resides within the galactic disk, attempting to photograph the entire structure simultaneously is physically impossible, analogous to trying to photograph a massive forest from deep within its thickest section. To capture the perimeter and shape all at once, an observer would need to be positioned light-years away from the galactic plane, looking inward, a viewpoint currently unavailable to us. Consequently, any image showing the complete spiral shape must necessarily be a scientifically derived model or an artist's interpretation built from decades of indirect measurements.