I often juxtapose playfulness with seriousness, yet it is quite possible for play to be serious — up to a point. Play can, in fact, play with most anything, but the spirit of play persists only where it has the last word; play can be serious, but it can never take seriousness too seriously. There can be, and often is seriousness without play, however; and this, whatever its practical value within the context of its parent worldview, is decidedly not a part of the Zhuangzian vision.
Allow me to suggest an example. If one believes that Reality has suffered some fundamental moral or ontological schism, as do all the world's religions (as best as I can tell), then one is required to get very serious in terms of at least personal redemption within it. Something must be done, or dire circumstances will follow. One will go to hell, or what's apparently nearly as bad, one will be reborn into existence. The revealed religions (Judaism, Christianity, Islam) see Reality as eternally sundered (God and 'his' creation are never One; God's moral nature requires eternal hellfire). The intuited religions (Hinduism, Buddhism) believe that it'll all work out as One in the end, though only after we have all become sufficiently serious about our individual redemption to allow it to be so. In both cases there is the need to get very serious about one's redemption.
Zhuangzian play could not exist in the context of such world-negation. Despite all the suffering that typifies the life experience, self-inflicted and otherwise, all is ultimately well, (and if not, outside volitional change). The human condition, absurdly magnified in its self-importance in the context of vastness, is no different than the rising and passing of stars or the decomposition of an overweight atom. "Handing it all over to the unavoidable" is an act of complete affirmation and openness, of entrusting oneself to unfolding Reality, where nothing need be done — not even that.
Zhuangzi's vision is of a purely optional affirmation of apparent reality; no eternal outcomes are at stake. Nothing need be taken too seriously. This allows the detachment necessary for all of life to become play; even the serious parts.
Seriousness without play saps life of its inherent joy, and what's perhaps worse, generally believes it is necessary to inflict itself upon all the world so as to sap the joy of us all.
You can check out Scott's writings on Zhuangzi here.