Does DRM contribute to this perhaps? Given the layers of encryption and obfuscation, and leaving aside the merits or otherwise of DRM in the first place, I can

Does DRM contribute to this perhaps? Given the layers of encryption and obfuscation, and leaving aside the merits or otherwise of DRM in the first place, I can imagine it could be hard to do delta patching. At least, without making it easier to crack the DRM - e.g. you’d presumably have to decrypt the asset that needed patching, apply the delta, and re-encrypt/re-sign it all client side.