-_- the number of artists may be increasing but the rate of production has decreased, yes?
If you mean that OYP doesn't have new pictures uploaded every 5 minutes even though there are this many artists, it's because there aren't many uploaders. Also, and I speak mostly about myself here, they might ignore some artists entirely for one reason or another, so they're not uploaded here. Finally, uploading stuff in the first place is a huge bother, and when you see new stuff that's top quality but is more than 100 pages, you're like "no man fuck this". If you look at the ゆっくり虐待 tag on pixiv (which is where abyuse is located), there are about 4 new galleries or illustrations every day, on average. The real slowdown is on 2chan, as I remember it used to have many new pictures a day months ago, but nowadays it's mostly just text discussions (or maybe I go there to often...)