Firstly, I discovered that some merits sources who also have good amounts of merits earned are denied of merits (maybe unintentionally) by other members of the forum.
I guess it depends on which sub-boards those members are active in. I like being in the technical Bitcoin boards. And in those boards you have maybe 20 regulars you can come across almost every day. We all receive and send merits (merit sources or not), and very often you end up meriting the same people. There are a few reasons for that. They are the ones who know what they are talking about and how to solve technical problems, and low-ranked users are hard to come by in those boards. And those who are there, usually have problems and and ask how to solve them. They aren't the ones doing the solving.
So if you are a merit source very active in technical Bitcoin boards, you will often come across quality and merit-worthy posts of other merit sources and high-ranked users. Usually, a high rank and being a merit source goes hand in hand.