A lot is due to Naturalism being true

The Natural universe shows no signs of being designed.  Least of all, designed for life.  Life as we know it can hardly survive anywhere in it.  And where we can survive, it is a struggle against nature/entropy:  starvation, extreme weather, other animals trying to eat us to survive.
Entropy may be vital to the very concept and possibility of a life form, and the "law" of increasing entropy may be a defining feature of a natural undesigned universe. [I haven't seen it discussed, but it seems to me that something akin to Newton's Laws of motion are required for the "law" of increasing entropy to hold. More specifically, maybe it's the symmetry of action and reaction, like in his 3rd law. Random musing, that symmetry makes the "arrow of time" seemingly disappear in physical laws themselves, yet the emergent behavior known as entropy is what people say causes the arrow of time to appear!]  
And it may be why information processing is needed at all, and why intelligence is needed at all.  Why bother with thinking if the universe just gave you what you wanted anyways?  And why would an individual separated from the environment ever come to exist if it didn't need to separate high entropy from low entropy? And like that thing I read one time, rather than asking why we sleep, ask why do we awaken? Why is that needed?
And, life is mortal, we have a limited time to work towards whatever degree of perfection or satisfaction we can.
Many of the important features of life are so linked to naturalism, even besides rationality.  Even among mere plants:
*[again] why would an individual (separated from the environment) ever come to exist if it didn't need to separate high entropy from low entropy?
*why would the living thing need to reproduce itself, if it were created by some god?  Our cars don't give birth, nor do they grow on their own.
*why have a species? Why not just one big perfect one? Or every individual completely different from each other?
*why consume food and produce waste? Why aren't they just artistic sculptures? Or magically alive despite no metabolism of physical substances from low entropy to high entropy?
Supernaturalist hypotheses turn out to be unable to answer these kinds of questions. At best they can make endless excuses (that often don't make sense). But without proof that the excuses are true, that just means they have the same number of questions to answer, but now they are all of the form "how do you know that this excuse is true?" And then they can't answer this new vast set of questions.