I have been writing high quality comments for main thread post but still no merits have been given

But you did get merits, didn't you? Since whether a post is of "high quality" is an equally highly subjective matter you can't expect to get merited for every post that has more than 100 words in it. Don't focus on the merits, focus on the content, try to learn things and give back your knowledge. This has far more value in the long run, for you and for the forum.