two reasons, names are not so good, or lack of promoting skills,
I found out it is better for you to develop some of the not-so-nice ones before sell them. you don't need to spend too much time on this, just 1-2 mon or so, and that will help you at least pay off.
buy a dedicated server, reg domains with potentials-->dev a site for each one in 1-3 mons-->sell it, usually make 100+$ on each name.