I think it is because in the creation the darkness preceded the light.
I am strongly YEC though I have a science background in my education including Modern Physics and higher Math.
IMO the greatest argument against darwinian evolution is math itself and the probability that everything (matter and life) came by chance out of nothing (The big bang and the Primordial Soup) is a statistical impossibility of pure chance given any length of time considering something called Irreducible Complexity
http://documenta_pdf.jmir.dyndns.org/Dembski_DebatingDesign_2006.pdf#page=370
Now, of course, theistic evolution solves the problem of Irreducible Complexity by introducing God into the evolutionary equation.
It is however IMO an unhappy marriage at many levels so I have decided to wait and leave the YEC problem areas unanswered until some later time when we can ask Him for ourselves.
I have no problem with those who see the Day-Yom in the Genesis as an undefined quantity/quality passage of time model though other passages in scripture fall back on the creation model of the 24 hour solar day model.
e.g.
Exodus 20:11 For in six days the LORD made heaven and earth, the sea, and all that in them is, and rested the seventh day: wherefore the LORD blessed the sabbath day, and hallowed it.
HankD
Jesus seemed to hold to Adam and Eve were historical humnas, crated not evolved, and still love what Luther said, when theistic evolutionists thinking strated even then, with denying literal 6 days, as he said that we should allow that the Holy spirit is wiser than us when he had tose verses penned down!