The problem with self-help "philosophy" in particular in the case of Stoicism — but also when it borrows piecemeal from Eastern traditions — is that it's completely divorced from its metaphysics.
Stoic ethics of 'living according to nature' was underpinned by an idea of a natural, rational cosmos (the "Logos") to which living up to is worth it. Nietzsche fairly devastatingly (expressed well in this comic[1]) pointed out that in an irrational and chaotic cosmos it's not the stoics living with nature, it's that the Stoics desperately attempt to project their own philosophy on the cosmos. A kind of psychological self-delusion and neutering.
And while most people who are fed up with self-help Stoics likely haven't read Nietzsche directly, I think they can intuitively smell that. The hollowness of self help gurus comes from trying to practice the ethics of a philosophy of antiquity without the metaphysics of antiquity that underpinned it. If you find yourself in a Lovecraftian universe living in accordance with nature does not sound so good any more and the Stoic self help guy seems more like a shoddy salesman.