I learnt from my experience that despite high PageRank, directories never acquire substantial amount of traffic from search engines. Can someone shed light into it? Is it because directories don't have common theme throughout or lack of content or both?
i think one of the reason is because theres alot of directories out there... tons and tons of competitors...
Yes I agree, lots of competition. Plus there are not many directories that do a lot of promotion. Some of the bigger directories will rank well for many of their category themes.
Directories are not made to provide traffic. They are created to help out site with the serps and PR and even get a new site indexed. If you submit to directories thinking you will get traffic, then you are there for the wrong reason. Directories have been known to help websites out in the serps, but not provide traffic. Most of the traffic to directories are just webmasters, not consumers or general web surfers.