“Only be sure that thou eat not the blood: for the blood is the life; and thou mayest not eat the life with the flesh.”
This is why digital meat thermometers are so important. 165 degrees for chicken or I don’t eat it. If it oozes blood it is not safe to eat. Possibly the above has to do with food safety?
I believe that it has to do with bacteria in the flesh. This is a CDC recommendation.
It's a superstition adhered to by most primitive peoples. They see the result of blood loss on the body and logically (though wrongly, of course) conclude that life itself is contained in the blood. It's one of the reasons why there are so many taboos, paralleled in cultures continents apart, concerning menstruation.