Before the fall there was no death. After the fall there was the sacrifice of the animals for the clothing. My understanding is meat wasn’t really permitted until after the flood. In Genesis 10 it says: And God blessed Noah and his sons, and said unto them, Be fruitful, and multiply, and replenish the earth. [2] And the fear of you and the dread of you shall be upon every beast of the earth, and upon every fowl of the air, upon all that moveth upon the earth, and upon all the fishes of the sea; into your hand are they delivered. [3] Every moving thing that liveth shall be meat for you; even as the green herb have I given you all things.
The why is speculative. I’ve heard different theories. Perhaps the need for a different diet following a big change in the earth’s atmosphere, following a world catastrophic flood, climate change. It’s not specificity said why.
Life expectancy went way down according to the geneologys afterwards as well.