I just don't like the feeling that nothing is a set reward for expeditions, dungeons, etc. You could technically get really unlucky for months and not get anything. At least with currencies+RNG you still get some surprises but you don't risk working for absolutely nothing. Feeling like I'm wasting my time is the surest way to get me to quit. If I wanted that feeling I'd go sit at a casino next to all the chain smoking grandmas and pull the slot lever all day.