It may have been for more practical reasons as well. There's reasons to believe the climate was temperate year round before the flood. With the introduction of winter, it would have been more difficult for early humans to survive on plants alone.
After the flood everything changed. It was not the same kind of world. Don't forget though that God had cursed the ground because of Adam and Eve. The prophecy was that after the flood, they would get some relief on the farming and growing of food.
Genesis 3 on the curse.
16 To the woman He said:
“I will greatly multiply your sorrow and your conception;
In pain you shall bring forth children;
Your desire
shall be [
a]for your husband,
And he shall rule over you.”
17 Then to Adam He said, “Because you have heeded the voice of your wife, and have eaten from the tree of which I commanded you, saying, ‘You shall not eat of it’:
“Cursed
is the ground for your sake;
In toil you shall eat
of it
All the days of your life.
18 Both thorns and thistles it shall [
b]bring forth for you,
And you shall eat the herb of the field.
Then the prophecy about after the flood
And also God again blessed Noah and family and told them seed time and harvest will not cease until the end.
Genesis 5
28 Lamech lived one hundred and eighty-two years, and had a son. 29 And he called his name Noah,[
b] saying, “This
one will comfort us concerning our work and the toil of our hands, because of the ground which the Lord has cursed.”
God’s Covenant with Creation
Genesis 8
20 Then Noah built an altar to the Lord, and took of every clean animal and of every clean bird, and offered burnt offerings on the altar. 21 And the Lord smelled a soothing aroma. Then the Lord said in His heart, “I will never again curse the ground for man’s sake, although the imagination[
a] of man’s heart
is evil from his youth; nor will I again destroy every living thing as I have done.
22 “While the earth remains,
Seedtime and harvest,
Cold and heat,
Winter and summer,
And day and night
Shall not cease.”