Well, no, I would not equate evolutionary neurology (which is what I'm arguing here, not psychology per se) with philosophy per se, only to say the logical rules of thinking had to be grounded in the same conditions of cause-and-effect that one sees in reality, only abstracted because it some sense our mental state creates a small universe of its own (which is probably where sentience comes into this) in which these same logical rules that guide causational processes are no longer tied to a concretely developing system.

But that's the problem. The fact that reason exists untethered in our own mental state allows us to use it to prove a great many things, and more importantly it is underdetermined, through chains of logic depending on different axioms different conclusions can be reached. Scholasticism was a great example of how this can become a grand and learned and complicated artifice whilst bearing little connection to reality. Given that we are finite beings, and given that we nonetheless have a constructed mental universe, it strikes me that the purpose of reason is for reductio ad absurdum, to eliminate that inconsistent with the root logic of existence, whereas positive statements must be stated through empirical means which, by consideration of Humean/Bayesian reasoning here, is by its nature a series of ever more refined probablistic statements.

Also science, in defining the field of maximum probability explanations for observed correlations in empirical experience tends to have the effect of also assigning probabilities to those things defined as 'how'. Both how and why are questions that touch on categories of causation, which is implicitly defined above only 'why' implies a level above the initial scope of explanation - a how questions seems to be causation within a defined scope or limit. It actually interesting to consider for example that the 'why' of life was, until the 19th century, generally defined as vitalism or some kind of force separate from those known at the time - gravity, electricity and magnetism - read Kant or Hegel or other German idealists and lot of the weirdness (and frankly on some level irrelevance) in their presentation of natural science comes from these presumptions of the age. The 'why' of life can be found, as can it be within any other system inside the natural universe.

Now when people talk about 'why' they mean an ontological why specifically, namely the purpose or meaning of the universe. In an obvious sense, the reason science cannot answer this is that its whole ediface is constructed on probabilistic, self-reinforcing observations within the closed system of empirical reality and our universe. However, rationality in the form of logic and its highly formalised and decontextualised applications in mathematics are in one sense grounded in reality - it is why we have evolved to be able to use them as they are useful for modelling our environment and come from and are made possible by the universe's causally predictable patterns occurring in our thought process. On the other hand, as Kant well documented it can easily break loose of its constraints and entertain purely hypothetical entities based on logical capacities - such as a being unconstrained by the conditions of reality around us - namely some kind of God figure. So in a trivial sense science cannot answer this question... but it is suggestive in two ways. First of all that it has repeatedly defied our pure reason in the past. The rationalist science of Aristotle, admirable and incredibly inventive in its way, was not able to stand the pressure of empirical observation which is well know. This strongly suggests that the probability of our being wrong on something which we do not know and has been constructed based on logical axioms that are ultimately rooted in well documented psychological and evolved states of assumed thinking (such as towards animism and spiritualism) which have benefited us in the past should be held with suspicion on probabilistic grounds. Secondly, the general drift of the evidential structure is towards a universe more grand and un-teleologic than ever, a reduced role for the importance of humans and human volition (if it even exists) and the fact that life in some way a complex arms race game that has been played between aggregating quanitities chemicals as a sort of fluke with little more meaning that that. On these bases I would suggest that they 'why' of the universe is probabilistically favoured towards a lack of meaning, and if that is true then any unveirifyable and sense-less statement about entities outside the ambit of empirical reality is essentially a meaningless question.