No I do not believe it is hard to make an established directory, and the best example I have is directory journal. Launched about a year or so ago, and it is doing great as their editors have been adding resourceful sites every day.

I think that if a user wants to develop a directory and establish it … It requires just as much as a blog does and sometimes more because blogs gain links quickly and naturally whereas directories doesn’t go the same way.

While many people fail at making an established directory is because they want quick money therefore they tend to not make as much money in the beginning, so either they sell it, or abandon it, but to maintain an establish directory such as keep adding new resources every day and still approving sites specially if you are getting a large amount is a hard task for one person, so you need an editorial team for that.

Hopefully I have cleared it up.