If only the game had a true endgame, an actual target or objective to work up to, then engineering and all that stuff would probably feel a little more enjoyable because there's a point to it all. It could have been powerplay - a competitive political game that encourages direct pvp and group coordination. But sadly that's been sort of left to "exist" with no ongoing development or refinement of the system and so it languishes, ignored by most. Wasted opportunity. Anyway, in most online persistent world games there is some ultimate tier or objective that you spend time working towards, whether it's raids in WoW or nullsec in EVE. Elite doesn't have that and so the grinding starts to feel useless after a while.
I think it does (have endgame content) and I don't see it as complicated or particularly obscure either.
The game starts with basic equipment and there is a natural tendency for the player to want to improve it. More offence, more defence, better jump range, speed, manoeuvrability, even just looking cooler in the eyes of the player. That's all progression and there is enough of it that that can be all there is to the game for many.
Then there is the desire to compete against and co-operate with other Cmdrs, explore, to support a faction, to improve the rate of progression (finding the meta for any given activity), these are all endless or effectively endless, the player can keep going until they have had enough.
A common trap some players following 'helpful' how-to guides fall into is to bypass the 'learning how the game works' part of progression play, only to find themselves with the 'best' gear but no thoughts on what they are actually going to do with that equipment. I think there is a significant overlap between these players and those that complain about grind.
imo figuring out how the game works is half the fun
