I’ve heard it’s literally this. Every asset is duplicated for every map or level it appears in to speed up load times and to make it easier for development teams to work independently on different maps without stepping on each others toes. Also the assets aren’t compressed for faster load times, especially on console. Don’t know how true it is.
It's pretty much a straight trade of load times vs storage— didn't matter back when games were streamed from disk, but it sucks now that they're installed. It's just that load times are measurable and often criticized, whereas no one really talks about installation size, except maybe to remark on it when it's unexpectedly small— for example, FromSoftware's Sekiro, which clocks in at just under 13GB.
for large "open world" games, you sometimes dupe things to lay out the data in memory to be near each other when the items are near each other in the world, so you can stream data in or chunk it in efficiently. If a player drives toward a city you have to be able to load all the buildings and mailboxes in without any pause. it isn't easy
