Because I would have expected for game development that it would be rare for majority of the large assets (art, textures, 3d meshes, video, sound, music) to change multiple times per day, so - to me - sounds like would perfectly suit a differential/incremental sync protocol, rather than treating everything as a large packed blob. At least that was the case for the game development I did.
And generally - you are correct. But builds made for specific platforms have all of their assets "cooked" for that platform - so textures shipping on PS5 are not in the same format as textures shipping on the Switch, even though they were both made from the same original reference file.