I really don't think people put much weight on what post-docs will be like when choosing their career. People just pick a career that interests them. Reproduction is not a concern for a typical 18-year-old.
Personally I thought about income prospects when choosing a career. In my experience women are less likely to do so, which makes sense.
(Edit: can't write more comments - it makes sense because women have the option to have children and are not expected to provide for the family financially).