Amadiro's hatred toward Baley and Earth is partly because of Giskard.
Giskard did this in order to divert the hatred away from Fastolfe and Gladia. After all, Amadiro could have done quite a bit to harm them, but Baley and Earth were much harder to reach. The Overseers are built so pretty in order to serve as sperm collectors.
As a stopgap measure until the hermaphrodite program succeeds. After all, Bander stated that Solarians didn't want to give up the pleasure of sex, and the previous book showed that they have no understanding of the concept - but might have an easier time with it when the partner is a humaniform robot. There might have even been some conflict between the people who wanted to fully abandon sex, and those who wanted to keep their robotic lovers.