I'm not well versed in celestial mechanics, but I see a lot of "we're in a black hole" comments so far, and I'm super curious as to whether or not we know why black holes prefer a direction of spin. Can you (or anyone, really) shed light on that?

It's not that black holes prefer a direction, it's just that they have a direction at all. It's one of the very few observable properties of a black hole.

If I'm following correctly, the "we're inside a black hole" idea is a major reach, connecting at least two unrelated concepts (black holes could contain baby universes; black holes have spin). But it's a really interesting idea and not obviously wrong.

Is inside the article:

"A preferred axis in our universe, inherited by the axis of rotation of its parent black hole, might have influenced the rotation dynamics of galaxies, creating the observed clockwise-counterclockwise asymmetry,” Nikodem Poplawski

I think it would be more that the entire universe is in a black hole spinning in a certain direction.

Exactly and anything new entering the spinning black hole is likely to inherit its spin.

Of all the mind-boggling answers explaining this direction-of-spin thing, they picked the one saying "Hey actually you know what, our entire (mind-boggingly large) universe itself is located in a black hole. That'll explain things nicely."

I mean the universe in a black hole is one of the more common ideas in physics, though we don't have any evidence for it. So it's not surprising people pick it up and run with it.

With that said, when the universe was younger things were way way closer so would it be possible for things like very early massive quasars to inject powerful magnetic fields in the otherwise dark universe at this time and bias matter falling into galaxies to one direction or another?

The convenience of black-boxy things!