I'm not sure if this is true because you won't get merit if your post is not constructive. Please understand that if your post is meaningless and does not help the forum, especially for newbies, you will not get any merit from them.

If it is not the purpose of the merit, why did they put it there when it is nothing.

Think about it: if you see a good post that helped you a lot, wouldn't you send him a merit? Yes of course.
And surely if you see that almost all of his posts are helpful you will admire him, and then you can say that he has a lot of knowledge, and you will respect him.