Nature photographers can spend weeks or months scouting out a proper locale, picking the vantage point, waiting for just the right moment (or collecting and curating hundreds of moments), and then doing (possibly) final touch-ups in a photo editor.

Their work is copyrightable, and it can be argued the only "work" they did was pushing a shutter button and maybe some touch-ups. Nature did the rest.

We extend copyright protection to them; it's difficult for me to see why we wouldn't extend copyright protection to AI-synthesized works on similar grounds.