The answer is silly. Humans work for the betterment of themselves and humankind ? Who's insane idea was that ?
But since Picard is an atheist, then the other way around is probably the right answer. He's a communist.
Maybe we'll have book that describes this attempt as a great experiment during the 24th century abandoned due to the need to actually trade with other empires like Ferengi.
Or maybe, humans simply do not use currency with one another. You can get a beer (ok, earth ale) free, but the replicator stinks or you can get an imported andorian ale, but you need to pay for it. The betterment of themselves stops at the first bar that serves non-human drinks.