User blog comment:B214/General Discussion/@comment-82.178.199.20-20170715103919/@comment-3435913-20170715185511

Perhaps he sees research like this as a waste of time and resources since it's not necessary;
 * 1) Angels who give into temptation become Fallen. Though this has been countered due to the "Baby-making Room".
 * 2) After falling, there is no apparent system to re-ascend, so there is no worry of former Fallen returning to heaven as full angels again.
 * 3) Fallen can reproduce as they are (with themselves and with other species), and there is apparently no evidence that there are fertility issues like that with devils.
 * 4) Because the Angel can only reincarnate the righteous and most holy, their main competitor for candidates would be with the Devils, who look for the strong. If they were only left the scraps, then there would be no point in it at all.
 * 5) Morally, if the fallen replenished their numbers by reincarnation, it may further create a divide between the Angels and the Fallen who are essentially the same species but mentality and emotionally different. If they started replenishing their own ranks, it would make it near impossible for the two sides to return as one race.
 * 6) With the establishment of the Three Faction Alliance, as well as alliances with other pantheons, there is no immediate need to bolster their ranks. Azazel not wanting war would have closed down any attempts to recruit other species as new Fallen.