With all the word around the timeline issues surrounding the X-Men movies following X-Men: Days of Future Past, MTV News has done a really cool image of the chronological order of the movies and their events. (SPOILERS) Fans are mainly confused because of the ending of Days of Future Past, I for one loved it. But it does confuse a lot of people and they are just wondering what and why that happened.
In shorter terms, because Mystique was stopped by Wolverine, Professor X, and Beast and they changed the future – all that happened in X1, X2, X3, and X-Men Origins were erased in the timeline and now never happened. So the events with Striker and Magneto never happened. Jean, Professor X, and Cyclops never died, and Rogue never cured her powers leading to her sticking around and being with Iceman. Changing the past led to seeing the future X-Men still together like they should be.
Here is the image: