I believe that the ratings system affects both modelers and downloaders. You can set your calendar by regular threads complaining about the ratings system. People rate files low just to try to retaliate against specific people. Relying on the low rating, a potential downloader may avoid a file that he would actually like. Swap files are free. There is no need to gauge (by way of ratings) how good a file might be. A user need only download and import the file, and try it. If he likes it, great. If not, no money lost. It was free anyway.
That's just one part of the problem. Another part is that the ratings system has driven away several modelers over time, resulting (obviously) in less models posted to the swaps.