Sorry for interfering with your topic even I'm not a merit source, allow me to share my idea.
If you want to hear my opinion, this would be my reason.
I will not choose who the users are, (if I'm a merit source) I will give merit those post that something contributed to the community and help a lot of people IF they deserve to have. I'm usually more interested in an open topic post that gives technical and fundamental advice related to crypto stuff. And, I will not merit old topics, more likely fresh topics much better.
But some users break this scheme of distribution of merites, leaving them with themselves and without sending them to anyone else. For what reasons they do not distribute them, it is not known, maybe they are just too lazy to do this, or maybe they are very demanding on the quality of posts and are looking for posts of the Satoshi level to evaluate.
Since they aren't merit source, probably they had a high standard of giving merit. If they got this merit because of worth it post, there's no problem. But it would be better if you will not hoard merit. It's different with me, I usually spent out when I got merit. We have nothing to do about this, their merit, their right how to spend with it.