The underlying thing was that the Beyond Light expansion revamped all of the engines light model. Destiny 2 runs on pretty old console hardware, and to do so, it doesn't dynamically compute a lot of stuff. There's a lot of pre-computed data, and lots of manual placement of light until it looks good.<p>Hence, a change in light model means redoing light for all content. By reducing a large amount of content, you claw back to the point where it is viable to do so in a single expansion cycle.<p>And that's just one part of the problem. I'm sure there's bit-rot creeping into game logic and effect-rendering as soon as you don't maintain a piece of the game actively. Add a few years, and you basically have to redo a lot of work from scratch because the active part of the game has likely moved on.