Where there's lack of spiritual fulfillment, you're almost always going to find dissatisfaction. After all, why would Stevens write a poem about finding what's "good enough" in life if there wasn't some sort of dissatisfaction underlying it? In short, the dissatisfaction Stevens talks about in "Of Modern Poetry" is the dissatisfaction of modern life in general. There seems to always be a war going on, global poverty is at an all-time high, and the planet is melting. It's these kinds of concerns that should make us turn to poetry to find some sort of hope in what we're experiencing.
Deep down, our man Wallace Stevens is a very dissatisfied poet who wants poetry to make everything better for him.
In "Of Modern Poetry," Wallace Stevens suggests that the work of poetry is never finished (like, ever), which means there must always be some sort of dissatisfaction driving people to write it.