It’s hard and it particularly slows down the asset production process which is already a disproportionately slow and expensive part of development. Way easier to let the artists go apeshit exporting everything at 8k and a billion polygons because storage is cheap in a production environment.
Compression could help in theory, but then you’d have to decompress assets on the fly which takes a significant amount of processing power. The industry is trying to reduce the latency of getting assets into memory, compression would be moving the other way from that.
If you’re conspiratorially minded then you might also conclude that it’s to prevent people from having another major live service game installed on base model consoles, making you more likely to keep playing the one you’ve already installed. A kind of walled garden effect.