Possibly new theory:
Mom and Dad created Jack on purpose.
No, that's not even accurate at all.
Jack was created by Skaia, Sburb, Sgrub, or whatever. He's a common element in any session of Sburb no matter what name it's given.
Karkat explains this all to John in the Ectobiology Lab, on
this page.
Go read
this post. It's informative. Specifically, this part:
The Medium is populated by a stock cast of characters and all those standard elements, plus the planets whose content is generated with each session. Different bandicoots and all that. The actors are scripted to perform by certain motivations; differences are caused by the players and their guardians interfering with Sburb's stock plotline.
Jack Noir is one of those stock characters, along with the Black and White Kings and Queens. He'll be in every game, with the same motivation: to eliminate the Black Queen and take her power.
Theory: Because Jade can seemingly see into the future, she fully intended to upgrade Jack and sacrifice herself as part of a greater plan.
No, that's not accurate either.
Jade didn't see her own death in her Skaia dreams. She sees John reading the letter she wrote for his birthday present, but did not know why he was so sad.
She was told her dreambot was going to explode by the trolls, but there doesn't seem to be any indication that she figured out why that was the case.