Okay, for a technical explanation, here goes: Every game has overhead. This is the amount of processor power needed to just manage the game. Every feature adds to the overhead. The overhead is paid for by the players, as are all things. If the $$ coming in from the player base is insufficient to support the feature, the feature isn't implemented. FoE is a larger than Elvenar and thus the cost of any feature is spread across a larger base. This means more features can be supported.
Now for some discussion.
First of all, the reason FoE is larger and more lucrative is because it has PvP and other aspects of direct combat. It, therefore, attracts a younger and more easily manipulated group of players (at risk of being a bit ageist here). So it generates, I suspect, a bit more $$ per player.
Second, FoE is not only larger and younger, it's more male dominated. According to an interview I read with some Elvenar product development guy, Elvenar is not only an older crowd, but 50% female, an unusual percentage in this type of game which is almost always focused on PvP or has some big, important aspect of it built in. Thus, the ratio of male/female is unusual. Women tend to be more laid back (according to a recent psychology report) in gaming and thus to spend less.
Third, Inno is a business. As stated in the opening paragraph, they won't add a feature to the game that can't pay for itself. So the sandbox, which takes up a lot of server processing, will probably not ever come to Elvenar.
Now, that's my take. I could be, as I sometimes am, completely and utterly wrong. Hopefully, some wiser and more knowledgeable one will correct me.
AJ