Why is blood removed from meat?
Blood finds use in many different dishes as well as biotechnological applications. Research-grade BSA (bovine serum albumin) is derived from cow's blood, there are not special facilities, same cows go for steaks and car seats. So part answer is economical: blood can be processed further. Also it is just easier not trying to preserve liquid inside vessel already opened by slitting the throat. It also seems that blood can rot faster than other tissues, maybe, because in dead animal immune responses are deteriorated and every infection in blood will activate.