Merit is a subjective thing, you can get it even from posts that only have humorous value in them.
This post is one example, do you see anything changes the world stuff from it? nothing at all. But normally merit will come to posts that are:
(1) Useful, and
(2) Helpful.
If you want to gain merit, make those 2 points as your main reference.
I am curious because I see posts that is more qualified for merits but ignored while lower quality posts at being merited or could it also mean there is favouritism in there?
Not all merit sources come from the same local board, or like the same things, maybe some like the mining section, maybe some like the economics section, or even gambling section. So, if you find & feel that there are some posts not appreciated or undervalued, you can report them in:
[self-moderated] Report unmerited good posts to Merit Source.