I would guess that most of your hires are single young people. And you are already kind of teaching them to work nights and weekends, which sounds like you are, again, choosing people who would not have a problem with a bad work life balance.
I also wouldn't be surprised if your process isn't teetering on the illegal side. Not on purpose, but it might be accidentally favoring or disfavoring a race/gender. Probably not enough to get you in trouble though, because those things are hard to spot. And unless your company is really big, probably nobody cares.