Factual error: If the Russian cosmonauts need special suits to survive out in space, so should Lacy when she is abducted by Nuclear Man. (00:02:50 - 01:20:20)
Factual error: When Superman addresses the UN, the delegate presumably representing the United Kingdom appears behind an "England" sign - "England" is not an international entity represented at the UN, while the United Kingdom of Great Britain and Northern Ireland is. (00:32:20)
Factual error: Superman places the nuclear missiles in the giant disposable bag in space, throws them at the sun, and the bag burns up when it hits the sun. In reality, the bag would have burned up long before hitting the sun. (00:35:35)
Visible crew/equipment: During the city attack, after Nuclear attacks a bus, a boom mic is reflected on a cab's windshield. (01:10:25)
Revealing mistake: When Nuclear Man destroys Metropolis, one of the walls between the window shop wiggles and the tiles flutter revealing it's a cardboard set. (01:10:55)
Continuity mistake: Clark grabs the crystal with both hands, and slowly starts retrieving his left hand. When the shot changes, his left arm is in a totally different position. (01:12:15)
Continuity mistake: The driver of the SWAT van disappears when the van is standing upright. (01:14:00)
Continuity mistake: When Superman is giving his speech outside the Daily Planet, the background is a clear blue sky. In every other shot of Superman, the sky has gone all cloudy. (01:23:45)
Continuity mistake: After lifting the car, for unknown reasons Superman has a visible dark blue bracelet on his right arm. (01:24:55)
Continuity mistake: After Clark reads the 'Drop Dead' cover, he stands up and walks down the newsroom, all puzzled. The number of people and their positions has no continuity at all between shots.
Continuity mistake: The same man next to Lois on the train is standing on the platform a second later.
Continuity mistake: After the "Drop dead" cover, Jimmy Olsen talks to Lois. In the close-up of Lois while she says "He looks like my father," the journalist behind her is standing up. An instant cut later, he is seated.
Continuity mistake: When Nuclear Man steals the Statue of Liberty, its pedestal looks normal. When Superman puts it back in place, the pedestal is missing a huge chunk (surely because of some FX going wrong). In further shots, it's fixed.
Continuity mistake: When Superman leaves Lenny at the school, a group of kids gather around the gate. On the far right there's one with a red hat, an Afro-American boy with a football, and one with a jacket who grabs the gate. A shot later these last two have vanished but can be seen in the background, metres behind. When the priest exits, half a second later, half a dozen more boys have appeared seemingly out of nowhere.
Continuity mistake: When Perry White dismisses Warfield, a woman in yellow walks towards the escalators. A shot later, the escalators are empty, and she is walking towards them again.
Revealing mistake: When Superman and Nuclear Man fall down the building, their capes remain stuck to their backs, defying the laws of gravity, and thus revealing that the scene was shot with them standing up and then turning the camera around.
Continuity mistake: When Moscow's Red Square scene begins, the tanks and soldiers parade in front of the authorities (a combination of matte painting and a real set). When Superman arrives, a second tree has appeared next to the one on the left. On the right side, an unfinished painting has replaced the previous huge wall, trees, and decor. (International theatrical, TV, and LaserDisc releases).
Visible crew/equipment: When Superman saves the day in Moscow, the edge of the set and the backlot behind can be seen on the sides of the wall where the politicians stand. One can even see the set's scaffolding on the right. (International theatrical, TV and LaserDisc releases.)
Continuity mistake: Before Nuclear Man finds the newspaper with Lacy's photo, he is at Lex's lair kneeling down, then starts to fly. Big clouds of smoke come out of his wrists, but an instant cut later in the close-up, the smoke is gone.
Revealing mistake: After Nuclear Man destroys the cab's hood, the shot changes and there's a thick string running behind him all along the car, and the cab driver is stretching out to pull it. Probably he was activating some sort of bad FX.
Answer: There appears to be multiple reasons. They had creative differences, ultimately resulting in a poorly received movie. Kidder said Reeves, who co-wrote the story, had an inflated ego and clashed with Furie.
raywest ★
Moreover, Mark Pillow, who played Nuclear Man, claimed that working with Reeve was quite intense.