I'm not an expert but that won't stop me from guessing why!
Perhaps it would be far easier for the donor to regrow the majority of their own liver in their own body than it would be for the recipient, given the immune response and other factors that I would imagine complicate a transplant.
Perhaps it would be far easier for the donor to regrow the majority of their own liver in their own body than it would be for the recipient, given the immune response and other factors that I would imagine complicate a transplant.