Back in Fantastic Four #123, Reed Richards conceived of a plan to finally rid our world of the threat of Galactus--by taking the world-devourer's ship hostage, and threatening to destroy it unless Galactus vowed to depart and leave Earth involate, forever. But Galactus came back with a deadly counter-offer:
Reed had no choice but to accept Galactus's terms. But he had one trick left up his sleeve, a part of his plan which he tried to make clear to the Surfer before the sky-rider took off after his master:
Chaos erupted, with no one understanding why Reed was apparently endangering the Earth by restraining the Surfer and consequently causing the return of Galactus, who might then reconsider his decision to leave and follow through on destroying all life on Earth. But, by mystic means, Reed addressed the people of the world and explained that the world need never fear Galactus again:
Things now look pretty good for Earth... for the FF... for the Surfer (well, maybe not for the Surfer, since he's still trapped on our planet)... but they sure don't look good for the inhabitants of the Negative Zone, since Reed has now dumped on them a destructive force that will methodically seek out their worlds to feed on, killing billions upon billions. A place which Reed seems to think very highly of, when his planet isn't on the line:
So the point where Reed doesn't "turn his back" on the Negative Zone seems to have one large exception--and it goes by the name of Galactus.
Which brings us to a somewhat negative
Marvel Trivia Question
Why did Galactus abandon the Negative Zone?
Imagine everyone's surprise when, two years after Galactus is sent to the Negative Zone, the alien being called Firelord arrives on Earth and announces the impending arrival of his master:
An announcement which has Thor voicing the same sentiment the rest of us are: "Huh??"
Even the man on the street (in this case, a reporter) remembers the previous encounter, and the fact that Galactus has no reason to even be in our universe again, let alone threatening the Earth:
Galactus, however, makes it clear to us that he means business--and it doesn't look like his stay in the Negative Zone has whetted his appetite for good 'ol positive universe worlds:
It turns out that Galactus, after his return, made another attempt to defeat Ego, the Living Planet--but he found that Ego in his absence had been driven mad, and so Galactus came to Earth seeking Thor to establish an alliance in order to bring about Ego's end. But that still begs the question: Why did Galactus leave the Negative Zone? I suppose he had no real reason to stay, unless upon arrival he found himself surrounded by worlds rich in life force energy and concluded that the Zone was definitely the place for him. If that wasn't the case (and it's indeed unlikely), he'd be in the same situation he was back on Earth: at a loss to find worlds in a timely fashion without a herald like the Surfer to act as a scout. So why wouldn't he immediately return, tell Reed "Nice try, but no dice," and take the Surfer? The way that writer Stan Lee ended that story was all very rushed and doesn't stand up well to scrutiny--and it should, given that this was a four-part story with plenty of elbow room for a more laid-out ending.
At any rate, we never get a clear answer from anyone as to why Galactus returned. The Thor story only broaches the subject in order to keep a sense of continuity, but doesn't otherwise deal with it. The only real answer we get--that is, if you want to call it an answer--comes from Reed some time later, when the FF is about to enter the Zone in an extended exploration:
It was an "explanation" clearly meant to leave the issue at that, and move on. I don't know why Galactus would be concerned with the "mysteries" of the Zone, any more than he was with the mysteries of our universe, since he has tunnel vision in terms of his hunger and is on a single-minded quest for new planets. Still, I'm guessing we're all pretty happy to have Galactus threatening us all again. We're certainly not going to hear the people of the Negative Zone complaining about it anytime soon.