So from what I’ve heard, or at least from the podcasts I listen to, it was created after the Tokyo Olympics in the 50s(?) and they kind of just landed on 10k. They say that, yeah the kanji symbol for 10k looks like a walking man, or that 10k has some form of symbolic reference.

I felt very justified when I heard that because my partner often said I shouldn’t aim for 6k steps a day, but hehehe, jokes on them.