What the vitalist valuation of life forgets is what Nietzsche himself says about the need for illusions to preserve life. For what does life need to be preserved against? —Against itself! We need illusions (ie. interpretations, values, etc.) to preserve in life because life itself (that is, bare life on its own) is horrendous and cannot be valued on its own. We require illusions (values) that affirm it. But taking life itself as the central value attempts to bypass this need for illusion, ending in nihilistic confrontation with the intrinsic valuelessness of life itself (i.e., existence rests on a void). Attempts to overcome nihilism through the valuation of life ends in another encounter with nihilism, even more virulent than the first (see: Ray Brassier's argument in Nihil Unbound).
In the end, a blind affirmation of life cannot provide an escape hatch from nihilism, or an overcoming of it through the transformation of "passive" to "active" forms.