Because what is the point if something is distributed in a restrictive license, can't be preserved and then gets lost to time? Also, licensing is to avoid distribution, modification or outright copying by competitors; preservation is completely orthogonal to those concerns. It is to avoid losing a piece of craft to the sands of time. There is no reason laws should have power over anything in perpetuity.
As seen in other spaces, pirates ignoring the "law" will provide the greatest service to humanity.
Laws are simply rules chosen and enforced by a given society. Having power over things is what they do. (Also, "in perpetuity" seems untrue, as all copyright expires eventually.)
You clearly disagree with the laws (and I'm inclined to support you there), but what is special about preservation that it should automatically override the will of society? Nearly all the combined work of humanity has been "lost to time," and society seems pretty okay with that.
Because it's the only thing that will be left of us in 100, 500, 1000, 10000 years. Whatever we care to preserve today will be what will be left to our descendants. It always matters more than the profits of some company today that won't be around in 10, 20, 100 years. And before you try to argue that not everything is valuable, that's fucking not up to you to decide for our descendants.
> Nearly all the combined work of humanity has been "lost to time," and society seems pretty okay with that.
Works that were lost through things like war, conflict, migration, etc. Not through conscious choice. Copyright is a deliberate decision to prevent the collective preservation of our modern culture in favour of enriching corporations and the handful of people who own them. But that doesn't make it moral or right. And "society being okay with it" doesn't make it okay either.