Why not simply...?

I understand that those letters were quite scaring to a family having little children.
But the real house did not have tunnels like in the netflix show.
There was no strange girl climbing into the bed in the middle of the night, that was just in the show.

So if it was only about those letters in real life and no one ever tried to attack the family or the house, couldn't they just ignore these letters?
I honestly think the person who wrote this letter was someone older who used to be poor and is simply jealous. But that person wouldn't actually to something in real.