Focusing on the small group of moderators♦ can be misleading in the way that small samples (4 users) are hardly ever representative of anything. This site is mostly moderated by regular users, as the statistics in 2018: a year in moderation show: for example, moderators♦ closed 181 questions last year, while the rest of users closed 3,123. As is often said, Stack Exchange sites are moderated by you (any user who earns reputation through participation).
Anyone with 500 reputation can access review queues, where the bulk of user-moderation activities take place. With that in mind, let's look at the users who completed at least 1000 review tasks of some kind: they have earned the Steward badge.
- Derek F
- David Reed
- glls
- Reshma
- Dave Humm
- Oleksandr Berehovskyi
- Adrian Larson
- Brian Mansfield
- Tushar Sharma
- Raul
- SF_user
- battery.cord
- Martin Lezer
- SE_User
- RCS
- Himanshu
- martin
- Santanu Boral
- Sebastian Kessel
- superfell
- Vigneshwaran G
- Boris Bachovski
- Eric
- Ratan Paul
- Mohith Shrivastava
- Chris Duncombe
- crmprogdev
- Vamsi Krishna
- Jenny B
- Boris Bachovski
- Samuel De Rycke
- Sergej Utko
(The badge page linked above also has user pictures in case someone wants to guess user gender based on those.) It seems to me that the demographics of moderator♦ candidates reflects the demographics of the part of user population who are active in moderation. Which makes sense: if someone is not using moderation tools they already have (review queue buttons), why should they be given more tools?
My conclusion is that looking for bias or barriers put up at the time of moderator election is not going to be productive: the demographic balance is already lacking in the pool of viable moderator candidates.