Yeah, who knows what their true refusal is? There could be a lot of things: sperm donors are already screened for what is effectively high IQ via interest in the process and university degrees; the women don't want to take the risk of being novel (risk-aversion about anything to do with a kid? that's never happened before...); the promise of the bank was a bit of a failure since by the time you've gotten so very old that a Nobel could've been awarded you are also so old your sperm is lower quality; etc.