Great question, I’m not sure off the top of my head though. Maybe this is really the annoying copying that ps4/5 do where you basically need twice the disk space when installing https://www.pushsquare.com/guides/why-does-ps5-ps4-copying-u...

Imagine you have a 1GB game, with a 500MB patch. To be able to play the game while downloading, you need the full patch space available. To apply the patch to the game, you need to grab the old 500MB, stuff it somewhere, and replace it with the new 500MB (in that order, otherwise if the update is interrupted, the game is screwed and you need to redownload the whole thing).