Without a detailed analysis of many different factors, it’s not possible to “lay blame” based solely on the information provided.
Could be untargeted traffic – including, perhaps, targeted traffic that is too early in the buying cycle to be ready to pull out a credit card.
Could be poor product images, or lack of product images.
Could be poor product info.
Design could be terrible.
Could be the “add to cart” button or link is too subtle and people miss it.
Could be too many products are “out of stock.”
Could be a terrible checkout process. Checkout form sometimes doesn’t work. Asks for too much information, or requires too much information, too early. Accepts PayPal (or Google checkout) only but no standard merchant account.
Prices could be too high.
Shipping costs could be too high.
Shipping costs may not be provided until after the user goes into checkout and provides credit card info.
Could be the “look and feel” and the overall presentation fail to inspire trust in the user.
Could be poor hosting, such that pages load too slowly, or sometimes fail to load at all.
Could be luxury products with very elastic demand, and no one’s buying those products in the current economy.
Could be there are competitors offering the same or similar products at better prices with free shipping and a better warranty.
These possible reasons are just off the top of my head. I’m sure there are many more possibilities.
A detailed analysis needs to be done of traffic sources, keywords, the competition, visitor paths, the sales funnel and checkout process, a/b testing with different designs, etc.