Because if you do that, explore, your screen becomes littered with a bunch of useless waypoints for places you've been to already. All this high tech wizardry I'm carrying can't keep tabs on which zinc plant I've plucked already?

And woe be unto you if you happen to wander more than ten minutes from your ship. That's a very sad run/jetpack/run/jetpack (stop me when any of this becomes boring and unnecessary) run/jetpack trek back.