This is because it allows editors to move clips around irrespective of time order (non-linear time), in contrast with linear editing [1] where you build an edit by assembling the master in sequential order (ie, by recording from one reel/tape to another).

[1] https://en.wikipedia.org/wiki/Linear_video_editing

Linear is videotape or film, as in you don't have the ability to access any part of the content; you have to move through the content to find what you're looking for.

Non-linear is digital, so you can hit any part of it you want. "Random access" might be a better term, but that's the legacy.