To begin with, like any ancient philosophy, stoicism has a physics and metaphysics–how it thinks the universe works–and separately an ethics–how it advises one to live, and judge good and bad action. The ethics is based on the physics and metaphysics, but can be divorced from it, and the ethics has long been far more popular than the metaphysics. This is a big part of why stoic texts surviving from antiquity focus on the ethics; people transcribing manuscripts cared more about these than about the others. And this is why thinkers from Cicero to Petrarch to today have celebrated stoicism’s moral and ethical advice while following utterly different cosmologies and metaphysicses. (For serious engagement with stoic ontology & metaphysics you want Spinoza.) The current fad for stoicism, like all past fads for stoicism (except Spinoza) focuses on the ethics.
Ex Urbe