Tl;dr: the game lacks, goal -> it needs one.
The game lacks the slightest goal to reach. You could say that the goal is to level up and hoard stuff, but it isn't because nothing happens if you don't try to achieve them. To prove that there's absolutely no goal is easy: just start the game, log in and see what happens: your char is standing somewhere and if you check back ten days later, nothing has changed. Basically every other game would have some notion that you should do something if you didn't do something for a while. An arrow showing direction, a "game over" message or "you got 5 minutes to do x or else...".
Why's it problematic that there's no goal and it's a sandbox world? Because then it's all the same what world it is. If we don't need to do anything but can do pretty much everything, it's no longer fallout world. It's just a world with fallout graphics and the rpg part in mmorpg fails. I guess the game part fails aswell because you can't lose or win, which is typical in games.
So why would we need a goal? Because if there was something players at least had to do or they could not operate in the game, devs could manipulate our gaming style to match how we should behave in wasteland. I dare to say that most players do not play the way devs had planned, or at least do not act in the game world a real fallout wastelander would act.
An example for a simple goal would be water. If you don't drink, you'll die. If you die in dehydration and respawn, you can't craft, use skills or fight. Where'd you get water? From npc factions or unguarded towns. To get water from guarded towns, you'd need good rep there. The ways to get rep is pretty stupid right now but it can be changed. It should be some favours that the players belonging to that npc faction may benefit. To get water from unsafe towns, you'd have to control the pump or pay a fee to the ones who control it. Now we'd have a goal. If you don't achieve it, you are punished by not getting to participate in every day gaming. You achieve the goal by either playing along with the rules of npc factions or having the firepower or caps to get it.
