I was kind of disappointed in Jack's lackluster response to Hurley's question. I've been looking forward to another great performance from Matthew Fox that I was used to. It should have been written better and the response "because I was broken" felt a little flat.
So I wrote my own response for why Jack is back with more to it.
HURLEY ASKS JACK WHY HE CAME BACK...
"I came back because the world we came back to, didn't feel like the world I remember. It didn't fit the same. I was lost when we got home. I needed answers to questions."
"Questions that came from this island. Things that I considered absolute truths were challenged during our time here. My father was dead but I saw him here on this island. I don't know if what I saw was actually him or a ghost or something else entirely. I saw a black smoke monster. I met John Locke who could be a completely reasonable man one minute to a man, who accepted from the second we crashed here, that something magical was happening and we were all brought here for some kind of a divine purpose. I could not except what he was telling me, I couldn't wrap my head around it. This HAD to be... just an island. There had to be a logical explanation for all of this. He begged me not to leave this island. He told me that I would regret leaving. He told me that he would show me a miracle. LOCKE told me he would move this island..."
"And we all saw it Hurley." "Still, I tried to forget about it, block that out too... anyway... we were on our way back home. Where we were suppose to be, right?"
"I tried to pick up the pieces. Cover up what happen to protect us from whoever staged our plane crash. Did such a great job that even I started to believed it. Went back to work. Tried to make a relationship with Kate. Then John came back, to reality, and he brought everything back with him. He killed himself after I blew him off again. I visited you, after your meltdown. You told me that Charlie said someone would come visit me too. And... I saw my dad again... I had a meltdown too. I couldn't get a grip on reality anymore. I came back here Hurley to make sense of everything. To get my grip on reality again. I need answers that can only be found in this place."
AFTER HE DISCOVERS HIS NAME AT THE LIGHTHOUSE... "Who's Jacob, Hurley? I find myself accepting the fact that you can communicate with the dead. Why does Jacob know me? Why does he know my personal relationship with my father? What my father use to say to me? Why was he watching me? What does he want from me?"
"WHY WON'T HE ANSWER ME!!" (Smashes the mirror.)