It probably has something to do with relative nature of how it is calculated?
As far as I can tell it gets calculated on basis of amount of models getting uploaded and amount of sales on them (connected to reputation score so prices of models is also relevant).
So if you upload models and sell them but the designers on top of you also upload models and sell them then there is no relative difference and rank stays same.
Basically one would only see difference when he is new and start uploading models, he then ranks up relative to those of similar profile (having same amount of models/reputation), he then would notice a leveling plane that keeps floating in same range (except when he starts uploading lots of new models and selling more relative to those of same profiles, or make more rep points by contributing in other way's).
I notice myself staying always in range of rank 210 and 206, sometimes falling back some points and seeing only some change when uploading new models or have relatively good sales. However it has been a while now sins I paid any attention to it because it basically has minimal relevance.
Maybe one can get some sense of how well some models/profiles are performing in terms of sales, other than that probably no relevance?
@limonadinis why do you believe this would make CGt unusable?