Why are women Uber drivers paid less than men?

Article here. From Feb. 2018 but a good article. Excerpt:

'STEPHEN DUBNER : So you write in the paper that unlike previous studies, you were able to, “completely explain the pay gap.” So can you unpack that just a bit?

REBECCA DIAMOND : Sure. Uber pays drivers based on a relatively simple, transparent formula that takes into account how long your ride is in miles, how long the ride takes, and potentially, a surge multiplier where sometimes there’s, excessively high demand.

JOHN LIST : So the fare itself is determined by an algorithm, which is gender-blind. The dispatch itself is gender-blind. And pay structure’s tied directly to output and not negotiated.

DIAMOND : That transparency and that simplicity of pay is what makes this environment so interesting for studying a gender pay gap.
...
DUBNER : So let me just make sure I’m clear. You’re saying there’s no gender discrimination on the Uber side, on the supply side, because the algorithm is gender-blind and the price is the price. And you’re saying there’s no gender discrimination on the passenger side. So does that mean that discrimination accounts for zero percent of whatever pay gap you find or don’t find between male and female Uber drivers?

LIST : That’s correct.
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We find that the entire gender gap is caused by three factors: a) experience on the platform (learning-by-doing), b) preferences over where/when to work, and c) preferences for driving speed.

This suggests that, as the gig economy grows and brings more flexibility in employment, women’s relatively high opportunity cost of non-paid-work time and gender-based preference differences can perpetuate a gender earnings gap even in the absence of discrimination.

It’s a pretty significant and important finding that has implications for the rest of the labor market — you can find a gender earnings gap even in the complete absence of gender discrimination that is explained by gender differences in preferences.
...
Overall, our results suggest that, even in the gender-blind, transactional, flexible environment of the gig economy, gender-based preferences can open gender earnings gaps. The preference differences that contribute to pay differences in professional markets for lawyers and MBAs also lead to earnings gaps for drivers on Uber, suggesting they are pervasive across the skill distribution and whether in the traditional or gig workplace.'