So I have recently tried a few other MMO's, a small list which includes Elder Scrolls Online and WoW, and I couldn't last longer than a few days in either of them. Although I don't have any data to analyze for DDO, I think it's reasonable to say that the populations in those games dwarfs our busiest time zones.
What plans currently exist to grow this game? How come I have never seen a DDO advertisement or commercial in the years I've been playing (this is not the same as saying they don't exist, I just don't know of any)? Why do people rattle off ESO, WoW, GW2, Diablo III, Blade and Soul, etc. when you ask them to mention some MMO's - but DDO is never mentioned? People don't seem to know about this product at all.
The beginning of this game is extremely unfriendly to new players. The text in the character creation is OUTDATED. It's awfully written, the attributes that are relevant to each class are not always straightforward. Asking new players to read for hours on the wiki isn't inviting.
In my opinion, throwing people who don't know how to play into korthos, without any hand holding or direction, drives players away. Nothing out there grabs them, makes it fun from the beginning, or gives the feel of a good dungeon crawl. For the first few levels, new folks should have their hand held. Then once they are a bit more familiar and comfortable, can they go off on their own.
Also, the enhancement trees look really complicated to the untrained eye, I think it can scare people away.