I've looked through 3/4 of them so far, and most of the failed projects here are actually because there was no market for the product in the first place. Then there is designing the product wrong (so it doesn't do what the user wants, or doesn't clearly do so), not having enough resources, and not charging enough money. Lack of focus on sales and marketing is an issue in a few cases, and in those few cases it can certainly be a killer, but it's not the most likely reason for project failure.
