In Star Trek: Enterprise, Archer saved humanity from the Xindi, but he didn't really care about the real enemy, the Sphere Builders.
In the episode Zero Hour, the crew of the Enterprise NX-01 destroyed Sphere 41 which started a chain reaction destroying all the spheres. But, the spheres weren't really destroyed if you think about time: they were still there in the Delphic Expanse if you move back in time.
The Sphere Builders altered the past to experiment one thing and failed to get the desired outcome. What could stop them from experimenting again?