Humans have basic instincts, motives and drives. They are driven by their biological programming and cultural conditioning to find ways to express these drives. They also have wired-in pleasure and accomplishment triggers that directly reward them for implementing certain actions in certain ways.
Beyond the biological, humans appreciate certain intellectual and achievement challenges in ways that don’t appear to be directly linked to evolutionary programming.
So the human is playing EVE because it gives them a sense of empowerment, or achievement, or effectiveness, or of being competitive in a positive way. It gives them a sense of accumulating resources, of accomplishing objectives against adversity, of being recognized for their actions.
Their reward centres are triggered by some of these actions so they are rewarded directly. Their addiction centres are triggered by some, so they are compelled to stay at it. Their need for social hierarchy and finding a place to ‘fit in’, an ‘us’ to belong to and an ‘other’ to eliminate, come into play as well.
For many there’s simply the satisfaction of solving an intellectual puzzle: setting up a decent industry chain, managing a complex trade empire, most efficiently clearing out combat sites, etc. These also feed the “winning, resource gathering, being more competitive than the other guy” needs as well as giving a nice intellectual experience, by the way.
You’ll also notice quite frequently on the forums, the people who play or post only for the opportunity to imply “I’m great and a winner and you’re shyte and a loser”. Because some people really crave the chance to express that in some parts of their life. Usually the ones who can’t express it any other way.
It’s not part of your OP, but in my opinion most of this stuff is what CCP just doesn’t ‘get’ about their player base. They don’t seem to clue in that players play to accomplish their own goals in their own ways, and they pay for the opportunity to do that. CCP seems to have the notion that “players will pay us because we’re the only game in town (so far) for this type of entertainment. All we need to do is channel them into the most expensive parts of the game and we’ll make more money! Hooray for us!”
The only real drivers CCP appears to recognize are “I want to be bigger and have more stuff, so I guess I’ll have to pay for more alts and buy more Plex” and “I already spent a lot of money on this game, I better keep spending money or I’ve wasted it all”.
Instead they need to be thinking “How can we make this game extremely engaging for more players by building as many of the things players are looking to achieve into the game and its’ base mechanics? Then we’ll have a great game that people pay for because they want to play it”.