I would like to know why are there so many embryos available in the first place?
In order to increase the probability of a pregnancy that takes a large number of eggs are harvested, fertilized, and implanted.
They may have to do the procedure several times, so they have a large number cryogenically stored. If it takes the first time and the parent(s) end up with all the kids they want, you end up with stored frozen embryos.