if you look back at their post history you will find like 4000 or 7000 posts are none of those weren't shitpost?
I agree to this part. Yeah, its true. It doesn't mean that a particular post is a "shitpost" just because it has no Merit. Some post are just being ignored by other Members that's why they can't notice that a certain posts is meritous.
There are 3 reasons (in my opinion) why a particular post can't receive a Merit.
1. Post being ignored.
Like what I said, some post are just being ignored that why it has no Merit. Although a particularly post is a Good Quality Post or Informative, if readers ignore it, then it won't really receive a Merit.
2. Because it is posted in Megathreads.
If you're one of those Member who always liked to post in Megathreads, your posts won't really receive Merit. It is hard to read post in such threads mostly if the thread is flooded with spam posts. Most of members who give Merits for Good Quality Posts doesn't visit Megathreads too much, that's why there is a possibility that no one Merit your post there. But sometimes, some Members do.
3. Spam post.
This is the common reason why no one Merits a particular post.
Besides that, about the other thing you were trying to say. I can't barely understand what you want us to understand. Or I'm just a little lazy to understand it.
I would add your list of reason why no merits will be earn. It might be possible that they are abusing new members just like they've been abuse by higher members in the past just like working in real life when i'm still a new workee they abuse me not because i did not do my job but because i am new to the job. The other reason is there are lots of alt accounts in bitcointalk, you see another name but behind the forum name it's still the same person that is why they won't easily give merit to your post or someone's post.