Sword Ban is world-wide or universal-wide?
I think the real reason is that Sorachi-sensei actually forget about it. Hell, he even forget about Shinpachi and Otae's goal of restoring their family dojo.

But, here is the interesting thing. After loads of episodes where Shinpachi and Otae's goal was forgotten, a new character named Hajime who was supposed to be Otae and Shinpachi's senpai at the dojo returned to Earth.

This Hajime returned to Earth after travelling to universe to learn various sword techniques and challenged sword masters around the universe. By this, we can safely assume that the sword ban was enacted only on Earth. As to whether it was enacted all around the Earth or just Japan we can't say for sure since Gin-san and friends never left Japan's mainland.