It's because it takes so long. Great to play online--just have to have the time and if you're in school or married...darn real life. Still awesome playing solitaire and by lan with friends.
I'm thinking maybe the Titans in Rebellion will be designed as an "end game" tech to speed up things.
I actually think if they provided moew gui-freindly methods of modding that aspect of the game would hook people in at home alone and then the modding itself would make them want a community and to join in online play.
The developers should really look at some of the tools being made by users--quite impressive.
https://forums.sinsofasolarempire.com/408652
https://forums.sinsofasolarempire.com/377772
https://forums.sinsofasolarempire.com/380961
...not to mention the entire library of Harpo's tools.
Simply tweaking and patching Galaxy Forge would be a huge step for hooking new players.