I think I already read this in other topics, but here's my question. I have five websites, and I've promoted them the same way. One of them reached the number one position for a good keyword, but others are really bad at SE. I repeated the formula for my successfull site, and the result was really bad, like all the others sites I have. So, at this moment, I earn 250$ from one site, and 5$ from all the other four sites combined. I know this happens with a lot of adsense publishers, only getting revenue from one of their sites, this even happens with some gurus out there. I wonder if this is some kind of tactic from google, not letting you be successfull with more than one site. If anyone has more than one site getting great revenue, please share them, or at least your formula.
I am doing good revenue from more than one site and as far as my vote goes its nothing related to Google but depends on your site content and traffic. Now about the sites not performing for Adsense can have lots of reason and one of them as it seems from your post is the traffic but the other could be that there are not many advertisers for the content and so Google is unable to deliver high paying ads to your site
The reason usually one site provails over the others is simple, that site is usually your first site that you put the most work into, as you develop new sites they don't get the original attention your first one did. This is common, you should spend an equal amount of time and work on all your sites evenly.
Presumably these other sites are not just duplicate content- if they are, there's your answer right there- so different content attracts different types and numbers of visitors, some niches are more competitive so you're fighting with more other sites for those visitors, your newer sites haven't aged as much... all kinds of possible reasons. Give it time, put some real quality effort into it, test...and see how they go. Good luck!
Perhaps you need to optimized them well. Do you have same number of visitors for each site? Probably the niche of your site is too competitive.