This is true, to earn merits you have to earn them from others and to do that you have to show up in sections where merit sources and generous merit givers read and post in, most of the members who earn a lot of merits make really good posts in a lot of sections. So if for any reason you make most of your posts in sections where the most generous merit givers do not have their eyes on, you'll probably go long periods without being merited.

I also believe your 'merit fans' and how popular you are is also important, there are certain members who would naturally like most of the things you post, and if you are so good or lucky enough to have a lot of your merit sources as merit fans, you'll be earning a lot of merits.