Well my guess would be that in the higher end applications, you don't see people using backgrounds as often as you do in Poser & DAZ Studio. I for example use Bryce, Vue & Cararra to CREATE backgrounds for my Poser images, not the other way around.  For that reason alone, I don't tend to download backgrounds to begin with, but some newbies need the backgrounds if they don't have the software to make their own like I do.

It is a miracle that curiosity survives formal education. - Albert Einstein