Why do we pass the boolean of the
SetActive(here);
and not just do
gameObject.SetActive = false;
?
Why is it a method instead of a property ???
Just a curious question 
Property is a method disguised behind a field-ish syntax. And because of that people might be led to believe that changing a value of a property is something computationally trivial - this is not always the case. It simply depends on the implementation of given property.
This is why SetActive(value); is a method and not a property - to communicate (to the programmer) that this action is potentially a costly one.