Are you personally frustrated by the fact that you can't get the merits you think you deserve, or are you asking the question on behalf of others? Let's say that this is the first question, and I will answer you very simply - most of your posts are in a board that is very specific and which is unfortunately flooded with spam posts - you will not find many who are merit sources and are active in that board, and even fewer who will look for good posts in megathreads.
Furthermore, the number of merits you see in user profiles are not those that they can share, but what they have received - there is something called sMerits and it is not visible in user profiles, although it can be calculated from the number of received/sent merits.