There are two parts, the in universe part and the real world part.
First the in universe...
Silver Surfer comes to Zenn-La and finds it seemingly under siege. The thing is, he can't come in contact with anything.
Eventually it is revealed in the issue that nothing is real.
Just what happened is unclear, since The Surfer was on the opposite side of the universe.
What is eventually revealed is that Zenn-La had fallen quite some time ago. The 1940s if I remember correctly (when the Surfer was still a herald). However, because Galactus had made a promise to Norrin Radd, he recreated it so that at least in some way it could go on.
So eh Zenn-La and Shalla-Bal he left were real, just not the one he returned to.
Real world answer...
So, the Silver Surfer was doing really well for a while. Quite possibly because Stan Lee's early stories and "no touch" status for over a decade (which was only rarely ignored) and a half created a deep respect for the characters, with most creators binging their A-game.
Enter George Perez's run.
He got very experimental (the Surfer got cut up and and body parts auctioned, with a little girl princess bug bringing him back together) at a time when the industry was collapsing. The story was readable, but probably not as good as it seemed on paper.
Either way, as the industry collapsed, anything that didn't have an X, Spider, or Hulk was in trouble.
Many books were cancelled, and any big name character from the 60s were set to be saved, exit George Perez.
It is important to note, this story started the same month as Heroes Reborn... another mark of unpopular editorial decisions.
When it ends the Surfer arrives on Zenn-La.
That is his last issue as writer. What he planned out as a whole is unknown... at least to me. It ends with us and the Surfer making the revaluation.
The ball is then handed to J.M. Dematteis, who at the time was more or less one of the the company's fixers (and a giant fan of the Silver Surfer, especially Lee's 1st six issues). Being J.M. Dematteis he ran with it as he saw fit in some interesting and metaphysical ways.
His run is really pretty good, the problem is he gets the blame for what started in Perez's last issue, because he had to play clean up.
IN reality it was probably neither's true goal since, it was about half a year until they actually got to the explanation. And much of that time had Glenn Greenberg as co-writer.
At the time, Marvel was doing a lot of back to basics stuff, Heroes Return being the most successful. The relaunch of Spider-Man and Hulk being the non-successful.
For Hulk back to Basics meant angry green idiot. For the Surfer, it meant hanging around around Earth, dealing with humans and mourning a lost world.
Again, the Dematteis stuff is really pretty good from issue 125-145... if you can get past the annoying retcon, which admittedly was handled interestingly, if not problematic by nature. Hard I know.
IN reality, after what Slott did to Zenn-La, I am more okay with that decision, which I hated when Iread it.