Why are forums thought to be not profitable?

[Val_Resnik]

I don't get it. I can understand why a purely off topic forum would be hard to monetize because the traffic is so random, but why are targeted forums hard to monetize? If I make a forum about mesothelioma, why shouldn't that be a profitable site? I don't understand why there is a general rule that says forums aren't profitable. Shouldn't it really depend on how targeted the forum's users are, how profitable the niche is generally, and how much competition you have?

[abbeyvet]

Forums tend to have lots of repeat users, who come for the forum and after a while cease to even see the ads much less click on them.

It isn't so much that they are not profitable, many are, but that you need a lot of users and a very focused forum to get a decent volume of clicks.

Forget about mesothelioma though!

[mack]

There are may forums that are very profitable. A forum is basically a very large content site. If your forum software can create search engine friendly url's that search engines can work with then your pages stand a good chance of ranking well for given key terms. Don't expect to make very much just through your members. It's the visitors who find you through search engines who are likely to click.
Repeat users get used to the ads and don't click very often.

Mack.