Here’s some other translations of Genesis 9:4:
(Leeser) “ But flesh in which its life is, which is its blood, shall ye not eat.”
(New American Standard Bible) “"Only you shall not eat flesh with its life, that is, its blood”
In the days before modern science, making sure the blood was drained from an animal was a sure way to determine it was completely dead. Without blood there can be no life. Leviticus 17:11 “the life of the flesh is in the blood” This also was a way to prevent cruelty to animals in not eating flesh from living animals.
Additionally, we need to remember that God is the Creator. He has knowledge beyond the best scientist or nutritionist in the world. If He gives a command, I would take it seriously. There may not be an immediate effect from drinking blood, but physical problems could grow over time. Blood carries waste products, bacteria and viruses. When an animal is diseased, the disease would be in its blood and passed along to humans. (In some primitive cultures, peoples would even eat their dead relatives and contract blood-born diseases.) Thankfully, modern science has helped educate people about some of the dangers inherent in blood consumption. But our knowledge about blood is foundational compared to our Creator’s understanding.
In summary, we may not understand all the reasons behind God’s commandments, but following His directions is always the wisest course.