Let me first start by saying, I love the game, it is a great achievement, and I enjoy playing it, but the problem comes from not having to play with anyone, I used to play with a bunch of real life friends, but problems within the game frustrated them and they got tired of it.
The game features some great qualities such as hardcore survival, good dynamic servers and massive worlds, but the reason for it's unpopularity is because it only targets a very small audience, of which being groups of people looking for a severely hardcore game, of which your sole purpose is to try and ruin everyone else's gaming experience, you can't play this game alone, you can't start off a new character in the middle of a current world, and you can't not know what to do.
Saying this, the game has some great aspects, I love the different features such as foraging, fishing, hunting, building, crafting, surviving. It features and amazing huge world engine in which you are dropped off in the middle of the early earth to build and live, for what purpose, no one knows.
The game has it's imbalances, some being the more you play the more you win, and others such as some times there is nothing to do, but the main reason I think it has a limited target audience is because of the developers inflexibility, I would like to see more range of the game spread out, such things as private servers, higher customization, more stable servers, maybe varying music other than the only two.
Love the game, don't hate me for my opinion. Also the lag drives me crazy. there are 60 people online :/
I want the game to be more popular, I think if the servers were more stabile, maybe private servers introduced. the game would be better.