Lore is good an all, but is all serve the much important immersion, once you have immersion, people will make up their own stories, along with a sprinkling of lore and a mission (other than "sandbox")
Like say in games like FFT/Tactic ogre or xcom, a nameless randomly generated character can give so much feels and bring you into the games. For tactics it was the likeable unit portraits and their dying messages (also randomly generated), xcom was the fact that they have country flags on their uniform.
Even say in homeworld1 and 2, when your ships are seconds away from exploding into fireballs, your captains still matter of factly and professionally proclaim their oncoming demise. (along with most all voice acting in that game, make you really feel like *** is serious and not a game)
FTL? Simple mission, everything else generated, so you somewhat care when your characters die, as every one is important to your success.
Immersion