Well, this is not exactly the way you're reading it. The merit sources are actively searching for newbies to merit. The issue here is more about the quality of the posts, this is difficult to find some quality posters nowadays.
Of course, after some interaction between the people, seniors members are used to merit those ones whose posts they find to be qualified for the task. Of course, this is a matter of probability: if you have been in here for a long time, and you are active and aware of the forum issues and circumstances, that's more probable for you to write something of use to the community. This is fairly normal, then, that senior users are the more rewarded ones.
But it doesn't mean that there are personal preferences, in fact, newbies should be more rewarded, for there are many people out there just looking for some newbies to reward. The problem is that there are few, actually, deserving it.