We can perhaps better understand this by examining Kantian doctrine, in which we find - surprisingly - this anthropocentrism based on subjectivism.

Indeed, Kant asserts that nothing is an end in itself, except the reasonable being, who must therefore be treated not only as a means, but also as an end (this is the second formulation of his categorical imperative): Man—and in general every rational being—exists as an end in himself and not merely as a means to be used by this or that will at its discretion ¹.

Everything else, i.e. everything other than man, and beyond that, reasonable natures (angels perhaps?), are merely means. If we are familiar with the relationship Kant establishes between value and end, we understand that this means that only man has an absolute value, while things and other beings only have a conditional, relative value. Relative to whom? Man, i.e. the centre of the universe: The value of any objects to be obtained through our actions is always conditional. Beings whose existence depends not on our will but on nature, if they are not rational beings, have only relative value as means, and are therefore called ‘things’ [Sachen]; whereas rational beings are called ‘persons’, because their nature already marks them out as ends in themselves (i.e. as not to be used merely as means) ².

Kant thus affirms this unheard-of proposition: only man has value: [persons] are objective ends, i.e. things [Dinge] whose existence is an end in itself. It is indeed an irreplaceable end: you can’t substitute for it something else to which it would be merely a means. If there were no such ends in themselves, nothing of absolute value could be found ³.

What is remarkable is that it seems that Kant uses a classic subjectivist argument, i.e. a Hobbesian one, to ground this idea: value is not in the world, but is generated by human desire: All of the ends—material ends—that a rational being voluntarily sets before himself as things to be achieved through his conduct are merely relative, for their value comes solely from how they relate to the particular way in which the subject’s faculty of desire is constituted ⁴.
Or again: Things that are preferred have only conditional value, for if the preferences (and the needs arising from them) didn’t exist, their object would be worthless ⁵.

In other words: this or that thing has value only because I desire it; when this is no longer the case, it loses all value. As we can see, Kant is developing a subjectivist position here. The answer to the question of whether Kant is a subjectivist will vary according to the importance attached to this passage.
If we think that here we find Kant's fundamental position on values, which underpins his whole theory of ends and duties, then we will say that ultimately the Kantian system is based on a latent subjectivism. If, on the other hand, we think that in Kant it is the concepts of ends and duties that are primary, and that this is no more than an ancillary reflection on a concept to which he attaches less importance than the first two, that of value, then we will classically think that the Kantian system is a formalist objectivism that inexplicably includes some subjectivist passages.

What does emerge, however, is the unprecedented anthropocentrism of creative subjectivism, which empties the universe of all its values, ascribing them to man and giving him the power to give them as he sees fit, to whatever he wants: One claims to call into question values, reverse or transmute them; in fact, one claims to create values, since the promethean subjectivity of man is considered to have an ability which, up to now, was attributed only to God: the creation from nothingness ⁶.

We can see that the condemnation of subjectivism as anthropocentrism, on the one hand, and as nihilism, on the other, already appears in Hegel, in a completely different context: for him, it is a question of condemning Fichtean idealism (Fichte's subjective idealism, not absolute idealism). We shall see how his critique intersects with ours.

1. Groundwork of the Metaphysics of Morals, 2nd section
2. Ibid.
3. Ibid.
4. Ibid.
5. Ibid.
6. J.J. Goux, Où vont les valeurs ?