Development of even the simplest video game is an extremely fluid process, and once you get into the AAA sphere, it's maddening how suddenly plans can change amid the hundreds if not thousands of moving parts.
As such it's no surprise that things get cut even extremely late in development, such as entire characters, levels, or storylines, yet due to the complex nature of production, developers often tend to leave the discarded data in the game files to prevent any unexpected coding issues.
And this is music to the ears of ever-eager dataminers, who are then able to dig deep into the game data and extrapolate cut content - content which can be in varying degrees of polish and completeness.
Sometimes the dataminers might even get lucky enough to uncover secret endings which were hidden within the game code, whether a fully programmed and complete sequence or simply vestigial assets from an unfinished segment.
While the developers didn't plan for you to ever see these endings for one reason or another, they were at least partially excavated by relentlessly committed hackers who enthusiastically explored the guts of each game...
10. Master Chief Finds Some Allies - Halo Infinite
Several weeks after Halo Infinite was released late last year, dataminers discovered the existence of a tantalising mid-credits scene which had evidently been scrapped by developers 343 Industries.
The scene depicts the Master Chief and the Pilot (aka Fernando Esparza) riding the Pelican as they intercept a message from a friendly ship.
The ship has a UNSC tag with the designation "friend," which is important given that the UNSC incurred catastrophic losses from the Banished at the start of the game.
This seems to suggest that Chief and Esparza will team up with the remnants of the UNSC to take on the Endless in the next Halo game - or it would, were this scene not ripped out of Infinite and included only in piecemeal, unpolished form.
Ultimately removing the scene does nothing to prevent any of the storytelling possibilities implied by it, but perhaps suggests that 343 wasn't 100% committed to this narrative direction yet, and wanted to give themselves an out in case they changed course.
Given that Halo 6 is likely many years away yet, it was probably a smart call to remove the scene if they weren't totally confident in the plot point.