Why did oop allow other instances of the same class to ignore access modifier?

Question

this is code.

class Node {
private int number;
int lotto = 3;

    public Node(int number) {
        this.number = number;
    }
    
    public void setNumber(Node node) {
        this.number = node.number; // why? 
    }

}

why OOP allowed this situation? I'm curious about your opinions.