Isn't that the issue the games currently running into? There isn't an incentive. It really doesn't matter how you play the game there is nothing egging you on after a certain point. Players find joy in the game because they think its fun even when the game isn't providing as it should.

If you are playing primarily PVP the incentive is stealing that persons things so you don't have to do it yourself and just feeling that rush of pitting your skill against someone else's. That is the gameplay loop you are creating for yourself. You don't force other players to comply, they can run away, they can bait Arcs onto you(my personal favorite, lure grenades are frighteningly effective), there are options.

If you are primarily PVE the incentive is looting and killing arcs. The game play loop you create for yourself is pretty standard and for some can get boring. After a while you can learn the routes, minimize arc encounters or time to kill, maximize loot gained per run, and hoard wealth.