If you were to read the Biblical passage, it becomes rather clear::::
Genesis 4:3-4 And in process of time it came
to pass, that Cain brought of the fruit of
the ground an offering unto the Etrnl. 4 And
Abel, he also brought of the firstlings of
his flock and of the fat thereof. And the
Etrnl had respect unto Abel and to his
offering:
Abel brought the firstlings and the fat, which is the best parts, while Cain only brought what was at hand, what was quick and easy. Abel worked for it, Cain was just being lazy. So, of course, Gd chose the delicacies over the commonplace. Why settle for leftovers when you can have gourmet?