If mutants can travel in time, why do they not change more events?

Question

In Days from Future Past, we saw how Kitty sent Wolverine back years earlier in time (1973) to prevent Mystique from killing Trask and thus stop the Sentinel program before it started.

Assuming that Kitty isn't the only one with the time-traveling gift, this could create chaos in the mutant world. Why didn't they change anything else?

For instance, Xavier could have sent Wolverine earlier in time and prevented the fight between himself and Magneto when they were young. This way, he could have prevented himself from being disabled and avoided a lot of pain. Also, Wolverine could have killed Stryker in that earlier time and avoided a lot of pain for himself.

And what about those myriad other mutants who are not related to X-men. What if one of those travels back in time and kills Xavier in his childhood? This could result in chaos in the X-men universe with multiple unexplainable and unrelated timelines.

Answer 1

In the film, the simplest answer is that Pryde's mutant ability is relatively uncommon. Additionally it requires Wolverine's mutant ability (itself incredibly rare) in order to allow time travel to take place over more than a few days span. When you combine rare with rare, you get ultra-rare.

Pryde : I can send someone back a couple of weeks...maybe a month but you're talking about going back decades. You have the most powerful brain in the world Professor, but the mind can only stretch so far before it snaps. It would rip you apart. I'm sorry, no one could survive that trip.

Wolverine : What if someone's mind has a way of snapping back? What if someone could heal as fast as they rip apart?

There's obviously nothing to stop them from continually changing time, aside from the lack of motivation on the part of the parties capable of doing so. Logan, for example would be highly unlikely to risk Jean becoming un-alive or accidentally reviving the Sentinels project.

Answer 2

In the Marvel Universe, of which the X-Men is a part of (Earth 10005), there is actually very little time travel. What happens is they create a divergent timeline and the original universe still exists. Even if they travel back to their original timeline, that's yet another new universe.

True time travel is something that happens only very rarely in the Marvel Multiverse. This means if that DoFP timeline was the original X-Men timeline/universe, then all those mutants who died to send Logan back actually died.

The divergent timeline method of time travel is handy as it prevents any time paradoxes from happening, except in those rare instances when someone manages "true" time travel.