Exacerbating the situation, Mario said, is the seemingly arbitrary placement of the hazards. "I could see why, if you're in a factory, you might find yourself jumping around on dangerous conveyor belts moving in different directions," he said. "But why would you have conveyor belts in a castle? Or in the middle of a forest?"
In Real Life, conveyor belts, escalators, moving walkways and similar conveyances are part of certain specialized environments, and serve the function of moving things in a convenient direction. In video games conveyor belts can show up anywhere: in the middle of a forest, in underground catacombs, etc. These belts don't move in a logical direction. They carry pedestrians into Spikes Of Doom or drop them down Bottomless Pits. Multiple conveyor belts move in opposite directions to trap players.
In short, the conveyor belt in video games often serves the purpose of hindering instead of helping its user.
This is almost always a sub-trope of Malevolent Architecture. (It could be some sort of Benevolent Architecture, but don't count on it.) Justified by the Rule of Fun, though it can get irritating on occasion, particularly when used with other, nastier hazards like Spikes Of Doom, Smashing Hallway Traps, Descending Ceilings and the like.
In top-down games, a conveyor belt will often act as a Broken Bridge, going too fast for you to be able to run against. It's a one-way trip unless you can find a way to shut it off or reverse it.
Occasionally overlaps with Conveyor Belt-O-Doom, which may get adapted into this trope in Licensed Games. Common feature of an Eternal Engine level.
Blue Dragon has conveyor belt puzzles, in which you will generally need to flip a switch to make them go the opposite direction, since it's not possible to actively move around on them, for some weird reason.
Castlevania: Chronicles of Sorrow (Castlevania: Aria of Sorrow)h as a habit of taking this trope and laughing at you with it. Conveyor belts are not all too common in the game, but once you meet them, they make you wish they did not exist. The belts alone are not dangerous, it is the combination of being attacked, risk of getting stoned and landing in a spike pit. Not fun especially since a stoned character takes a crapload of damage from the spike pits.
Chips Challenge: Among the hazards is conveyer belts, frequently leading either backwards in the level, or into another, more fatal hazard. At least there was a powerup (suction cup shoes) that let you ignore them.
In Mega Man 2, a large number of the platforms in Metal Man's stage work as conveyor belts, including the floor of the Boss Room.
And Flame Mammoth for those who played Mega Man X.
Those who have obsessively played the classic series will think of Knight Man's stage from Mega Man 6 and Proto Man's castle from Mega Man 5, examples of conveyor belts being located in castles. Then again, not much beyond hand waves have ever been given to justify stage layouts in the series.
Video Game/Mr.Robot features many of these obstacles around the ship Eidolon. Sometimes they seem to serve a sensible purpose like transporting boxes, but others just...there for the puzzles.
In Rockman 4 Minus Infinity, there are two sections are dedicated to these in Dust Man's level. The first one had debris falling onto it. The second had holes in them; luckily, Eddie points them out to you.
Moon Crystal, mines have conveyor belts hanging usually midair.
In Pepsiman, the first part of the Pepsi Factory area is entirely running along conveyor belts that run in either or neither direction while dodging things sliding along or falling onto them, as well as avoiding the inexplicably placed Bottomless Pits.
Persona 2 has the Abandoned Factory which is full of random, still-operating conveyor belts. Some seem to be logically placed in loading areas for moving heavy items to and from storage, while others exist just to provide one-way paths blocking off sections of the factory, teasing you with their presence until you're high enough level to open the doors into those other sections.
Portal 2: Most conveyor belts have an ostensible function ("The Turret Redemption Lines are not rides. Please exit the Turret Redemption Line."), but one in particular, late in the game, is deliberately set up this way as a Death Trap. Or, as the Big Bad puts it, more of a "death option", as opposed to confronting him in his lair, where he will most definitely kill you. If you wait, he spends upwards of three or four minutes trying to convince you to fall for it, and is very pleasantly surprised if you do.
Inverted in Hydrocity Zone. Sonic doesn't run on conveyor belts; he hangs from them, and uses them to get to places he couldn't reach without their presence.
Exaggerated in Death Egg Zone. Some of the conveyor belts are moving platforms which Sonic must take to progress, and they're designed to change direction whenever it's most inconvenient in order to push him into wall spikes or throw him into big ol' bug zappers.
Eggmanland from Sonic Unleashed had super-fast conveyor belts pushing you backward, as well as laser walls along the belts that you had to jump over or duck under. The bombs that were carried along the conveyor belts.
Casino Paradise Zone from Sonic Advance also has these. It's a rather strange place for conveyor belts, isn't it?
Casino Night Zone from Sonic the Hedgehog 2 was apparently planned to have these, as they can be seen in the most famous beta version of the game... wait a minute, they're in the final too, they just look different!
Final Egg from Sonic Adventure, anyone? THESE conveyor belts also tried to move you towards dangerous things, most of which were sharp.
One of the last two levels in the Game Gear spinoff game Tails Adventure had one or two of these at the start.
Super Smash Bros. Brawl: This is one of the items placeable in custom maps, giving the player the option of placing them inconveniently when building a sadist stage.
TaskMaker: One of these shows up in the tutorial level. The game instructs you to go over to a switch to turn off the belt. Interestingly, this actual trap only shows up in one place in the game — and all it's blocking off is a small pile of Skeleton Keys amid loads of garbage.
Ultimate Stuntman: It is not explained why in walking sections, there are conveyor belts hanging mid-air and just being out of place.
Wario Land 2 had a few of these, mostly in the factory levels.
As did Wario Land 4, also in the factory levels (annoying when at one health and trying to climb a set of conveyor belts with enemies on), and Wario Land: Shake It!
Non-Video Game Examples:
Animal Yokocho: Non-game example: in this anime, Mr. Yamanami fixes up Ami's room to be a jungle with a hot spring-sauna deep within. After Ami realizes that they've been walking an illogically long distance within her room, the camera zooms out to show that they'd been walking on a treadmill the whole time.
The board game Robo Rally takes place in a factory, so the belts have some reason to be there. However, some of them are arranged into swirling maelstroms of death which tip anything on them into bottomless chasms. (To say nothing of the pushers, crushers, lasers, and radioactive goo.)