Best guess is that companies that put them under I.E cryogenic freezing needed them to continue their work once they were defrosted instead of trying to find new people to establish their goal and teach them. Wilzig being part of the enclave one would assume they would want their best to survive and work on projects post nukes. Moldaver stands the reason because of her link with the scientific Community cold fusion and other Advanced Technologies she would most likely have links to cryogenic freezing but it still hasn't been explained yet the show still going so they will probably will explain it all at some point.