It was a fact, not a decision.

Equestria no longer needed anypony to bear the Elements of Harmony. So six mares suddenly found themselves in a position of incredible freedom. True, they all dreamt of a purpose outside of sitting around in Ponyville, waiting for an attack. They all had talents that could benefit elsewhere.

But everything isn't perfect. It never is.

Related to this story, but it is not necessary to read that.

Spoilers in the comments, so beware.