Why is northern Eriador (Lake Evendim, Fornost) deserted at the end of the 3rd Age?

[Elmo]

However, I imagine it more like visiting an old monument of Arnor, an act of piety. I don't actually think there would be something like evil ghost-haunted area in there. It is only the superstitiousness of the Breelanders to say that it is a haunted place: of course, because there was a big battle long ago, something evil (Witch-King) resided there for some time, and so on. But I would imagine even if some evil spirits lived there, the Rangers would go and clean it up ASAP. Sounds nondúnedainish to me to leave the main city of their ancestors unhallowed, if they had no problems with cleansing it (unlike for example Morgul, which was occupied by armed force - but in the end, we know that Aragorn did the same, I imagine this would be a similar situation).

If they managed to cleanse Fornost why did the not cleanse the Barrowdowns? Aren't they much more holy and revered because they held the remains fo the Dunedain's ancient ancestors.