we are talking about things that are actually taxing.
having lots of physics objects in one place is taxing. we don't know the full scope of how crazy it gets, but if you can have hundreds of things just lying around in your ship at all times, then that will hammer the CPU.
meanwhile Horizon has less complex physics and a more empty world than GTA4

which is why it's a terrible example.
the number of objects supported at any given time and the tick rate of the physics is unknown.
maybe they really want to make sure that you can just fill your whole ship with stolen plates or some shit... I mean, that's maybe a bit pointless but would explain why that old ass engine is a bit stressed doing that.