You seem to be ignoring the linked study, which found that female bus and train operators earned less because they took more time off and worked less overtime.

You seem to be ignoring the linked study, which found that female bus and train operators earned less because they took more time off and worked less overtime. Pay gaps due to reasons like these don't create arbitrage opportunities. You want people to work overtime when you ask for overtime. In general, the pay gap due to discrimination is much smaller than the total pay gap. It's also not universal: it varies by city and occupation. If you're evaluating two employees who seem about equally qualified and one asks for a 30% lower salary, it's easy to see the arbitrage opportunity. But if the employee is only asking 5% less? It's less obvious. You may have felt from the interview that the other candidate was 6% better overall. Then consider that discriminatory employers may not be evenly dispersed. In towns without much discrimination, there may be no arbitrage opportunity. In towns with heavy discrimination, there may not be enough non-discriminatory employers to hire all the undervalued workers.