Genesis 7:2

Here are necessary orders given concerning the brute creatures that they were to be preserved alive with Noah in the ark. He must carefully preserve every species, that no tribe, no, not the least considerable, might entirely perish out of the creation. Observe in this: God's care for man. Doth God take care for oxen? 1 Corinthians 9:9, or was it not rather for man's sake that this care was taken? Even the unclean beasts were preserved alive in the ark, that were least valuable. For God's tender mercies are over all his works, and not only over those that are of most use. Yet more of the clean were preserved than of the unclean.

Because the clean were most for the service of man; and therefore in favour to him, more of them were preserved and are still propagated. Thanks be to God there are not herds of lions as there are of oxen, nor flocks of tigers as there are of sheep. Because the clean were for sacrifice to God; and therefore, in honour to him, more of them were preserved, three couple for breed, and the odd seventh for sacrifice, Genesis 8:20.