This is a fanmade purpose it is not canon or probably won't be canon. https://www.youtube.com/watch?v=IjvL-BgNv_Q
Now you know how at the end of season 1 when Mirriois and the rest of the gang put Master Bill in a black hole or some shit? Well in season 2 Master Bill is back. However, how can he be back if he already died a tragic space death? Well in the beginning of season 2 Bolt and the rest of his crew try building a space ship to reincarnate him they spent months on it but it still didn't work. That was, until, they found Glaxia. When they reached that area the ship sent out Master Bill 2.0, just as planned. However, how is it that the ship took them to Glaxia and once they were there he was reincarnated by the ship? Well here it is, his crew never actually did make it anywhere. They all died and went to space hell, aka, Glaxia. They all died of accidents while in the ship, such as falling over, wasting air, and etc. The ship was brought with them as well. Master Bill was rebuilt once they got there because master bill was already in there because he died' So you might be wondering, how did Mirrois and the rest get there? Well Mirriois, died of fighting a Boss Enemy, the boss didn't just kill him himself, it made him sick and broken. After a few days of his friends trying to recover him, he, sadly, died. Now just so you know, once Mirriois entered Glaxia, like Master Bill's crew and shit, he couldn't remember how he died, none of the people their could, they were all trapped thinking it was a new place. All of his friends and stuff later died of suicide, or other causes.
All of the people in Glaxia are dead, this is why there are no humans there, and thus explains why Master Bill is alive.
Thanks for reading this theory i hope you had a great time! ( ͡° ͜ʖ ͡°) Stay tuned in for the next sidestory, Gamzee's adventures in Pop Star and mushrom kiondgdom!