If I had to make two guesses, one would be the average length of your posts.  While most of them aren't exactly up-to-your-asscrack short, I would bet that a lot of people with merits to give will see a lengthy (and well-organized) post as being more constructive than a shorter one.  That's not true in all cases, of course, and I'm also not a mind reader but it's an assumption based on all of the merited posts I've seen over the years.

The second thing is that a lot of your posts are in Bitcoin Discussion, where everybody's brain cells go to die.  I did not check to see how many pages the threads in which you made your posts had, but that section is one of the ones that has a lot of spam megathreads--or at least it used to; I don't know if that's still true, but it's always been hard to earn merit there.

I check the merits stats page a few times a week to make sure I'm not falling too far behind being a merit source, and I'm always amazed that DdmrDdmr is seemingly pinned at the top of the list.  Even with all the PMs I get for post reviews, it gets hard to keep motivated to spray merits like a fire hose after a certain point (or maybe it's just me).  Don't know how he does it.