As I understand it, there is a similar situation legally with regard to copyrights, trademarks, etc. If you don't enforce them, eventually, they are no longer

As I understand it, there is a similar situation legally with regard to copyrights, trademarks, etc. If you don't enforce them, eventually, they are no longer considered valid. Note that IANAL and I haven't investigated this in depth. I think the idea is that most people aren't computers processing laws as if they were code; most humans have to primarily go by what they see happening around them in order to decide what is ok. If they see lots of cars going down a road, eventually they assume that it is public property, even if they never check the public records to see if it is. Similarly with lots of other things. But, crucially to the Supreme Court's majority decision, you have to have a law saying that this is so (for real estate or intellectual property or whatever), for it to be so, and Congress never did that.