I call this the "poor for life" syndrome and some of the main reasons for that are self doubt, lack of information and piracy.
The low self-esteem leads them to believe that what they do is worthless and nobody will pay normal price for it.
Most of them also have no idea for how much they can actually sell the model.
Not paying for the expensive software they use also contributes to the inability to understand the real value of the model.
All this accumulates over the years as more and more similar sellers enter the market and everyone tries to undercut one another.
Some realize how pointless this is after a year or two and give up, but their low priced models remain on the site and make the next wave of similar minded sellers think this is the price they should aim for... and here we are.