Blood essence was valuable. The blood pond would be fed with treasured materials every now and then to create blood essence for disciples of the Lu Family to absorb. Someone that was not a disciple of the immediate Lu Family or that was not that talented enough wouldn’t be qualified to get into the blood pond.
It was because there were so many treasured materials in the pond that usually people could not absorb too much blood essence. The more talented the person was or the higher the realm the person was at, the more he or she could take in.
If warriors of low realm or of less talent forced to take the blood essence in, those ones would die because their body could not contain so much. Or they would experience extreme pain and pass out.