Eve is better described as a love letter to the military and related simulation games of the late 1980’s and early to mid-1990’s. They were complex beyond belief, required manuals in the 100’s of pages, had keyboard overlays because almost all the keys did something, and were quite vast in what was available to do in them despite the hardware limitations of the era. The programmers dreamed big and pushed the hardware to the limit.
As as a fan of those old sims, from my perspective it looks like someone took the code from several, attached it to a database, then said “what if we let other people interact with each other…” Eve’s heart is in a past era where the limit was pushed not necessarily to sell millions of units, but to see if it could be done. That’s probably why I enjoy it so much and why I am so glad I was introduced to it a few years ago.
Per the original question, the status of Eve as a niche game and why it doesn’t appeal to mainstream players is precisely because of its nature and the evolution of games since the time of those sims.
If I go buy a PC game tomorrow, I’m more or less guaranteed that:
1: It will work with a controller with a limited set of buttons and/or a touchscreen.
2: Needed documentation is handled by a simple diagram in the box or the game.
3: Gameplay concepts are covered by in-game tutorials or steady progression and in some cases the tutorials can be accessed from in-game menus for later reference.
4: With persistence I can reach the end goal or accomplish a satisfactory outcome without unexpected resistance, barring the occasional bug or crash. Progress can usually be measured each session.
Remove any one of these, or rely too much on the persistence of point 4, and you lose most of the mainstream interest as current mainstream players likely did not have to suffer the indignity of finding the keyboard overlay or the piece of paper or part of the manual that had the code to get past the copy protection on the diskette in order to even play, let alone figure out the command line. That required patience, something which in casual modern gamers is mostly lacking.
I don’t see Eve making the evolutionary leap from Bethesda’s '89 Terminator to Fallout 4 to attract the casuals. It would require too many trade-offs to map everything to just a controller, provide a structured narrative and play-through tutorial to introduce all mechanics and their activities, and provide sufficient direction to help those who normally don’t live in the narratives of their own mind along the path while still catering to those with the initiative to make their own stories within the rules.
As such, Eve will likely remain a niche game for a very specific type of gamer, and as long as it does well at that, it will do fine.