Isn't that the million dollar question any website owner wants to know.
The fact that dmoz.org is one single website, leads people to think there's one single answer.
But there isn't a single answer, and usually there can't be.
Any website owner can ask me (an ordinary surfer) why I didn't visit that site this week. (It's only a sixty-four-cent question, of course.) The answer is of the form "I was on some other site, or experiencing real life."
Now suppose I start editing at the ODP. Ask me the same question, and ... get the same answer.
But at the ODP, a site doesn't HAVE to be visited by me, to be listed. Thousands of other editors could have visited it. And each one of them could be asked the same question, and would have to give the same answer. They too visit other sites; they too experience real life.
So, there may be a million-dollar question, but the answer has a thousand parts. Nobody can answer more than one of those parts, and no single part is useful to the website owner.
In fact, no single part is useful to anyone but the person who can answer it...and, when you think about it, no single part is anybody else's business!
A lot of people seem to think the ODP is a kind of market research organization: its mission is to find out what sites, or kind of sites its editors visit--and report that to marketing corporations. But it's not anything like that, and it doesn't DO any of that. In fact, it's the exact opposite: volunteer confidentiality is EXTREMELY important.
Think of it like a beehive near a clover patch: how do you tell which clover blossoms will be visited? How can you know that some clover blossom wasn't visited, because a flap of a fruit fly's wings affected the air currents in a neighboring hemisphere, so the bee wobbled to the next blossom over?