You're treating it like well-established fact that people's career choices are based on gender identities which are fabricated by the environment they're raised in. Where is the evidence for this? Where are the oddball societies with female construction workers and all-male nurse workforces? If this is just an "accident" of the memetic evolution of societal gender tropes, then why is it so unilaterally consistent across cultures that have developed separately?

The biological explanation is, by far, the Occam's razor null hypothesis here. To be convincing, you would need to supply compelling evidence that children who have unusually low contact with traditional societal influence early in life make less predictable employment choices. Otherwise, this is a just-so story like all the rest of them.