There is both an artistic element & a social element to Renderosity. For some people, the social element takes precedence. They might comment on & praise a piece because they feel the creator is trying as hard as they can & though they may not have the skill or talent to create professional & polished art, that they should be encouraged. Or they might feel that because someone praised their work, that the sociable thing to do is to reciprocate. Or maybe they're doing it for selfish reasons - because they think their own work will be viewed & commented on more.

Personally, I don't think any of those practices are particularly helpful, but that's just the nature of social interaction here. It's perhaps more common in galleries like Bryce & Poser because they are low cost programs that many amateurs & hobbyists commonly use. Other galleries, like 3D Studio max, Cinema 4D, Zbrush, etc, tend to have a higher proportion of professional users, because they are pricier programs that most amateurs can't afford. You can complain about this kind of thing if you like, but that's just the way it is & I don't think it's likely to change. And there are still plenty of excellent Bryce artists here whose work I continue to admire & enjoy...

"Every child is an artist. The problem is how to remain an artist once we grow up." - Picasso