I watched a video where huge portions for the data of Team Fortress 2 and Fallout New Vegas data was deleted. Despite being reduced to tiny file sizes, the games kept running (even if they were virtually unplayable) and only crashed if data from a few critical files was removed. Why can games run when literally most of the game by it’s files has been axed?

If you think about what the majority of files in an installed game are, this should make intuitive sense. The smallest part of the installed game is the executable that runs the game. Then you've got animations, audio, textures, level geometry, pre-rendered video, and so on. Consider - while you're playing the game, at any specific point in time, do you actually need all of those assets at the…