I have a headcanon but after pink was shattered the diamonds realize that they could possibly be shattered and in order to prevent they're Utopia from being friends again they set out to create a back-up plan if any of them were ever shattered , using the human zoo and the moon base , They basically task 3 pearls with raising the hybrid babies and keeping an eye on the earth in three different locations ,, But until 20 or less years ago they had been unsuccessful with their experiments ,, aka they didn't realize babies had to eat and all the intricacies of raising children to adulthood .
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