Why does software have such extreme orders-of-magnitude variability? Anyone's guess. I like the perspective that software is made out of many pieces of little software, which are in turn made of even more smaller pieces of software. That fractal nature is a qualitative difference to people, which are not made of many tiny people. (As far as I know.)
You can know really well how long a light person will take to do a thing, or how long the camera will take to find an angle. Knowing when your client will move their arse to send you the test_data.csv is very much unknowable.