I'm not involved in the military, but it feels like there's an expectation that if you put in the work and meet the requirements, you'll get the promotions. I'm sure there's exceptions, and people problems and all that, but the expectations are there.
There's also (at least) historically been limitations on combat positions for women, which does limit certain types of promotion, because it's hard to meet the requirements if you can't get posted to the right kinds of jobs. That puts you in a situation where a tech job might be a viable path to promotion. And the military is usually good about training, so if you get into a tech job, you'll get trained to do it right, etc. (Or at least, that's what it seems like to an outsider)
There's also (at least) historically been limitations on combat positions for women, which does limit certain types of promotion, because it's hard to meet the requirements if you can't get posted to the right kinds of jobs. That puts you in a situation where a tech job might be a viable path to promotion. And the military is usually good about training, so if you get into a tech job, you'll get trained to do it right, etc. (Or at least, that's what it seems like to an outsider)