If someone blows up your ship, they destroy and steal real value that you spent time earning. Suddenly all that time spent being bored and grinding weighs on your mind when you contemplate a fight. It means you actually have something to lose.
Consequently, PVP in Eve comes with a shot of adrenaline. On top of that, there's an incentive to raise the stakes even more in PVP: spend even more time/money on better ship equipment and you have a better chance of winning (at the cost of making losses even more devastating).
This also means having allies is a real thing. Not just buddies who play with you, but friends who you rely on to keep you safe, and that rely on you doing the same. It really brings to the surface feelings of comraderie that I can only imagine one must feel in the military.
The big alliance level stuff is awesome, but it takes months to play out. The daily experience that keeps people coming back is very similar to the rush one gets eating spicy food: it hurts a lot, but it gives an incredible rush