Day by day, new members keep registering everyday. Only few of this member find it easy to rank up. Imagine an account opened for more than 2 year that still exist as a newbie. These are some of the reasons I observed why some of these people may find it difficult to rank up:
From another POV, some newbies may not be concerned with ranking up or even earning merits. That is another reason why they are not ranking up. I do not think that every user who has joined this forum is focused on ranking up to be eligible to promote a project on the forum by wearing their signature and avatar, or in bounty projects. Some are just here to really learn for a short time, and since they know that they will not be on the forum for long for some reasons, they do not focus on merit earning or ranking up.