All because Goku forget a piece of paper.

Now that I think about it, Future Trunks's world would probably have been FUBAR'd even if Zamasu never happened. Since Future Goku was dead, he never would have befriended Xen'o, which would mean no Tournament of Power, and Future Xen'o would have erased Future Universe 7 along with the other weaker universes as was originally intended.