Board Thread:General Discussion/@comment-4504826-20160516034744/@comment-26072045-20160526023919

It was initially Chara who had the power to reset. I think you need to be Underground and (possibly) have a red soul in order to reset. Flowey REMEMBERS what happens, but he doesn't actually have the ability to reset. The only ones with that ability seem to be Frisk and Chara.

Anyway, the reason I think Chara didn't reset is because they didn't WANT to come back to life. They wanted to be carried above ground so that the humans would encounter Asriel and chaos would ensue. Chara died to start a war. I'm guessing they figured that if they waited long enough, a time would come when they could find a human to manipulate into destroying everything.