Due to various complex reasons, on average more men than women treat income as a strong "hygiene factor" and are more eager to abandon fields that are nice in other aspects but have weak pay in favor of less respected jobs with larger pay. For example, if some high-skill/high-education profession starts earning less than taxi drivers or construction workers, then a larger proportion of men than women would abandon that respected high-education career and start driving taxis or painting walls to ensure better pay, causing or increasing a gender imbalance in that job. So I would expect that the decision to abandon their studies just because PhDs become less useful for generating income would be (on average) somewhat correlated with gender.