Well, Perez invented that certain mechanic. Previously, the gods never gave Diana powers; only life. She was born an Amazon who was said to be a match for the gods. Her powers came from a combo of purple fire and being an Amazon.Some people have suggested that the clay origin lie was necessary to explain Diana's powers, but I don't think this is true. Saying (falsely) "Diana, because you were the daughter of the queen of the Amazons, the Greek goddesses (or Gaia, or the universe, or whatever) granted you great powers" works equally well with a clay origin or a bio origin.
Maybe, not every Amazon does it. It could be that a select group of Amazons do it every time.(2) If the Amazons consider murdering their sperm donors to be a natural part of their culture - appropriate and justified, from their point of view - why is Diana just learning about it now? She's an adult; she talks to other adult Amazons; surely it would have come up. Why would it be a secret on their island?