Originally Posted by
rutog98
It happened because when Magneto is a villain, Marvel obviously has a policy that any character more powerful than him has their power levels adjusted downward whenever they face him in battle to prop him up to look tough. Its called PIS (Plot Induced Stupidity) and WIS (Writer Induced Stupidity).
Here's the thing, the sun has an EM field a trillion times stronger than the Earth's own planetary EM field. The Phoenix Force even feeds on stars. The attack Xorn used on Phoenix Force Jean Grey should not have worked under any circumstances as that kind of power should not have been able to hurt her. Its nowhere near strong enough to even scratch her back.
In the Phoenix and Dark Phoenix Saga, Phoenix Force Jean Grey had the ability to restrain and cut itself off of part of the Phoenix's power. Read Uncanny X-Men #125. Also, when Dark Phoenix killed itself on the moon, remember, she was not at full power. It had just broken free of the restraints Xavier put in Phoenix Force Jean Grey's head to restrict the amount of Phoenix's powers she could access. She still needed time before she could get up to full power and killed herself before she did. However, even if she were at full power, we know from Uncanny 125 that she can block off some of the power from herself if she wants to. Either way, she did not do this to herself to make herself vulnerable to an attack from Xorn. It was nowhere in the text and it would have made no sense for her to pull something like that. In other words, she was just written down here.