Symmetry… nothing more. There’s an innate human attraction to symmetry.
I was just reading an article about it. While reading and looking at the image - it is also very simple to make (carve). A cross would be the most simple, but the swastika adds a bit of flair without too much extra trouble.
I also thought of the sun, and that was mentioned for one of the cultures. Another culture had it as the connection between heaven and earth (one segment pointing up, the other down). For Odin I think it was to portray walking or spinning as he travels the earth.