Or because state property is state property. Just because someone isn't actively using something doesn't mean it's now free for everyone else to just take.

The shipwreck could last decades(theres a sailboat shipwreck near where i live and its been there longer than ive been alive. No active preservation is going on with it)or even longer if just left alone, allowing many people to visit it and see it. If people start to take it apart piece by piece than soon no one will be able to see it.