They always talk about blood having to be "poured out on the ground" and the blood of Jesus being "poured out as a sin offering" on behalf of mankind.
But Jesus blood was never literally poured out, and the blood poured out as a sin offering was never intended for Christians to do.
Most of all, as has been noted, David and his men ate meat with the blood in extremis, because the symbol is less important than the life itself.