Its a marketplace, driven by consumer demand.  A vendor needs to sell x of an item at price y to make a return. If he sets the price low he has to sell more of that item.  The question then becomes how many can he sell in say 30 days.

 

Poser stuff has been very inexpensive for a long time with a few vendors able to attract better prices.  As a digital product at least there is little overhead with making copies for sale, just the disk space to hold the source file.