This is because you can not scan of a single picture. Highly professionals can build a camera Array (very many camers placed in a circle that shoot the object in the center at the exact same time) that is able to process those Images to a 3D objeckt with textures. But mostly 3D scanning is done with Hand Scanners, Lasers, deph sensores… there you Need to have the physical object to scan it.
In my case i use Kinect 2 from Xbox One connected to my PC to scan people. Windows 10 has a app (store) that’s named “3D Scan”. Here’s what i do.
But the short answer is that you can not upload pictures to get a 3D model.