It is surprising really, how under developed the whole space sf game scene is. Especially when SF itself is so popular in other mediums. I guess that thanks to old JRR and giving some nasty fairies some good PR, elves have never been more popular and that is currently reflected in today's gaming fashions. I was gutted when Star Trek online went down the fantasy/theme park route (Just changing Orks for Kingons and the like) and had not gone for the "5 year mission" feel with a game that could have rivaled Eve and could have left Elite Dangerous having to play catch up with two established space opera type games.
I think it's underdeveloped because it's
hard to make these kind of games, and if they fail they tend to fail spectacularly.
Balancing issues are just so difficult to resolve whilst retaining some modicum of variety between ships. Most sandbox/mmo/whatever type games focus mainly on gear selection for a character, and due to sandbox games avoiding character classes there are usually (somewhat) limited styles/approaches that you can take.
In a sandbox space sim you have multiple different ships, different fittings for those ships, escape/capture mechanics, PvE income/hour rates, money sinks...
The economies of these games alone are wildly difficult to control, Eve's is quite simply mind boggling! That said though, in the last few years it looks like some developers have finally realised there's an untapped market for this kind of game. Even if ED and SC don't pan out, I suspect some AAA developers will be working on something to mop up the shattered remnants of their fan bases.