ED's downfall is exactly it's vast universe, cos it's empty. This is emphasized by their aim to be "realistic".
ED is like playing COD/BF maps totally alone. Not even with bots. All the game mechanics are still there, the graphics are there, but there is nothing to do.
There is no sense of place. It is an insanely huge world, but the variety is so limited, that every place feels the same very fast. Everything in the game only exists to serve a basic purpose.
Stations/outposts = main menu for trade/missions/repairs
Planets/moons = nav point
Ships = targets/set dressing
Asteroids = click to gain money/set dressing
Star = fly around for fuel/nav point
That's it. Everything is as minimal as it can be.
The way all these are represented was outdated from day 1. It's like pictures in a dictionary. Basic accurate representations, nothing more.
Ships don't have any fun articulation or any action outside of being bricks (ignoring the basic landing gear and weapon deploys which is not that interesting after 10 seconds), planets are just balls of blue or green, moons are smaller balls of brown, even from up close. Stars are kinda cool looking sometimes, but that gets old very fast as you travel from system to system.
There is no sense of self. You were your ship at first, then you were a basic bitch mobility scooter, and now you are a generic character in generic suits with generic sci-fi guns. But you are still not Your character, that freely moves around and does whatever it wants in a world. There is no "filler", where you can just walk about and do whatever. It is a tiny bit better now that you can actually go up to the generic shop on the generic station to buy your generic equipment, but that's about it.
The gameplay loops are hollow. You spend 95% of your time traveling between nav points, waiting to access the next menu, whether it's for missions or trade. For foxs sake, the most interesting part of the game is turnin off all the aids and landing on a station. If you have a tiny bit more patience then a 6 year old, it's easy, and takes annoyingly long after the first couple of times, so it's back to fully aided flight. You can even just push a button and autodock.
There is no payout in terms of time invested vs profit. Long term goals like getting high enough reputation and buying a large high-end ship takes waaaaay too long, because the grind is insanely boring.
The multiplayer just doesn't work. First off, there is nothing to do in MP apart from a few types of missions (kill ships, reach interaction point on ground). Even if there was, the way it works is so cumbersome, and it's more broken than what we have in SC when it comes to actually putting ppl in the same instance. You can't just "be" on the same server and do whatever you want together.
Ships lack diversity. And I don't mean in color... You can basically do the same things (trade, fight, mine) with almost every ship. You can do it slightly more efficiently with more expensive bigger/better ones, but getting a bigger better ships only means you can take more damage you or can fit more cargo. There is no equivalent ot a Prospector or Cutty Red or Reclaimer here. Almost every ship can be outfitted to do any of the few gameplay loops there is, and thus is the same. This severely limits progression, as there are only two types in the game: earning credits to buy better ships/equpiment to be more efficient, and earning reputation to unlock better ships/equipment to be more efficient. That's it. There is no such thing as "earn enough to buy a Mole so I can mine with my friends".
This in the nd leads to no incentive for progression. Why the heck should I keep grinding away to get X if all I can do when I get it is the exact same grind I'm doing now, without anything to show for it.
It's not like you usual mmorpg where you do the same grind, and then earn loot so you can grind more, because there is no challenge. Even if there was, there is nothing justifying the challenge. There is no story background which would incentivize the player to tackle the challenge (think raid bosses in MMOs). There is no epic loot to be had to show off for your efforts. There is no social points to be gained. Putting in effort doesn't have a payoff. The grind is there, the reward for it isn't.
In SC, when you start out with your 20k credits and an Aurora, there is no way in hell you can complete the 890J mission on your first try (if and when everything works as intended, which is like never but that's besides the point). It is a challenge that brings some clout with it, and a substantial reward in credits (and later, reputation). If you can honestly say you did it, it means you put in the effort and others will know. Same thing if you can earn enough to buy a Prospector. It's a big deal, because now you have something entirely new you can do. The reward is more substantial then just earning credits... You get what I mean.
tldr.:
ED lacks presence of self, presence of space, story, goals, progression... The only thing it has is menus, literally a handful of the most basic gameplay loops, and an oversized empty void for a universe.
disclaimer: I bought ED on launch, enjoyed it for it's basic stuff for a while and couldn't get back into it ever since, even though I try like every 1-2 years. I really try to like it, but it's just soooo boring!