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.
If it is reasonable that someone needs to preserve something because it has been abandoned, then the thing should automatically be in the public domain.
If you are not actively using IP for a reasonable amount of time, any patents, trademarks, copyrights, etc should be permanently expired.
This fixes problems with patent trolls too: you effectively would not be able to own a patent unless you were using it in your business.