The warp is a realm that is separated from reality by a barrier, keeping denizens from interacting with each other Daemonic possession allows for a daemon from the warp to take possession of a human body as a host. It involves a ritual in which a human is sacrificed to the daemon, with ancient symbols carved into the flesh to bind the daemon to that particular host. These binds enslave a daemon to a master and force it to obey commands, allowing the mage to retain limited control over its actions.
The problem is that even though a daemon is bound to a host, it is still susceptible to the same daemon weaknesses, such as holy weapons, holy symbols, etc, etc, which allow it to be sent back to the warp. In addition, the daemonic essence eventually corrupts the body of the host, ultimately destroying it. Over time, the form becomes more daemonic, adopting features attributed to the daemons true form and making it obvious that the body is possessed. The daemon is forced to expend more energy to retain the body and prevent it from breaking down completely, cutting down on its effectiveness.
To get around this, an ancient cult devised a millennia-long eugenics program. Over thousands of years, they would practice selective breeding among their members, recruiting outsiders when necessary or obtaining genetic samples through other means. The end goal would be to produce a perfect host for a daemon with the correct genetic makeup to contain it with no issues. This host would have all the benefits of daemon hosts with none of the weaknesses, and be able to maintain the daemon long-term with no issues. After this child is conceived, a ritual would be performed in which a daemon would take possession of the embryo and be born in the human body into the world.
This project ultimately proved successful. However, with advances in technology, the cult believes it can speed up the process for future possessions. The creation of the artificial womb has allowed children to be grown in batches, drastically cutting down on time and effort. Genes can be taken from a variety of parents and be mixed and matched to create a person with the correct genetic makeup. The cult has the financial means and influence to create facilities where embryos can be created all at once, with those successes being brought to term and failures being exterminated. This would allow them to create an army of daemon hosts quickly and cheaply.
I need a reason for why a millennia-long eugenics program would be a more preferable option of creating a erfect daemonhost, despite advances in reproductive technology. Why would natural birth be lead to the most successful outcome?