Because the authors of the text couldn't be talking about something which no one of the time had any knowledge. It's like expecting the writers of Genesis to be able to write about the topography of the Yukon Territory.
Divine inspiration does not mean that God gave to the writers a supernatural knowledge of a scientific process which would not even be known for many, many centuries later when it would have benefited nobody--because nobody who would have read these things in the times they were written would have been able to make that kind of connection making those points in the text entirely useless as Scripture for a pre-modern people.
They are made in "kinds", that is, in their diversity. The author does not attempt to spell out "pomegranates, apples, figs, mustard, rose bushes, tulips, wheat, rye, barley" instead the author simply says "of their kinds" that is, of the many kinds of [known] plant life, of the many kinds of things that swim, of the many different kinds of things that fly, etc. This is not about the development of thing after thing, but of the diversity and array of different sorts of things within the grouping listed, "things that creep" "beasts", etc.
-CryptoLutheran