If the extension of the question of purpose continues on in an infinite chain of reasons that all depend one each other, then there is no motivation for everything as that would imply an end to the chain of reasons.
I do not object, necessarily, to the suggestion that an infinite chain of dependent reasoning is flawed. I certainly doubt anyone would argue along the lines of his example that the creative consciousness created us like a nail to attach to boards and that the creative consciousness needed to nail the boards together to build a cosmic treehouse and that...ad infinitum. There is, however, an underlying problem with the reasoning, particularly the way the poster views concepts like "purpose."
The warrant for the entire argument seems to be that purpose can only exist if there is an end and that end is not fulfilled in creation. I would argue that the idea of an infinite being (which, for the sake of argument, we will assume the creative consciousness is lest we need to posit a further creative consciousness above each temporary one) precludes any ultimately finite ends. The purposes of creation would need to be infinite to correspond to the one purposing them. More importantly still, the suggestion that an endless purpose lacks motivational force seems to be radically disconnected from the more basic elements of the human condition. Our thirst for purpose is infinite, and purposelessness runs contrary to our most deep-seated desires. Even if you want to argue that humanity has fabricated deity in order to construct a more transcendent purpose, that still reveals ultimately that we have an eternal desire for purpose that corresponds quite neatly to the prospect of an infinite purpose.
I realize that I am about to drift away from a critique of nihilism and into a sermon, but the application is necessary to demonstrate the viability of the Christian religion on this point. Properly understood, soteriology is the appropriation and actualization of an infinite purpose. In the Eastern tradition, salvation is spoken of as an infinite ascent into deifying light. It is a purpose which inexhaustibly renews itself, and thus indescribably fulfills the infinite human thirst for purpose.
In short, my objection to the aforementioned reasoning is that not only would an infinite being necessarily create with an endless purpose but the endlessness of that purpose corresponds well to humanity's desire for purpose such that there is no need to fear a lack of motivation.