First of all, mods aren't responsible for giving out merits--the community as a whole is.  Second, whether you earn merits or not depends on basically two factors, 1) Whether your post is good or not, and 2) Your post has to be seen by someone with sMerits to give.

If you're posting in a thread that has many pages of replies, and I don't have a hard number for this, no one is likely going to even see your post.  Certain sections like Bitcoin Discussion and the entire altcoin section are full of spammers just posting to get paid.  Since anyone with either a brain or sMerits to give is going to avoid those sections, posting there isn't likely to do you any favors. 

You're fortunate to have gotten as many merits as you have.  Many members with your rank and post count have gotten ZERO merits, and they're not likely to earn any for the rest of their miserable careers on bitcointalk.  It's not supposed to be easy to earn merits; that's the whole point of the system.  If it was easy, it wouldn't prevent shitposters from ranking up and the whole system would be useless.