When the merit system first started, people were giving them out freely. I rarely see posts with merits on them anymore though - I guess most users have distributed everything they had to give and they've run out.
This subforum is pretty much the only place still giving merits out.
I have also observed this and I am not sure what has happened to merit sources. I rarely see posts getting merits in meta now. As per my experience, if 10 merits were being given in an hour when the merit system was introduced, now only one merit is being given per hour. I am talking about the meta section specifically. Other sections like bitcoin discussion always got less merits.