What I'm wondering is, if this is the explanation, why don't we see this more often? Plenty of galaxies have formed from mergers, right? So the question is, how much of a difference between the black holes does there need to be for this to occur? The video seems to imply only a small one, in which case one might expect this to be a common occurrence. So why haven't we seen this before? Or is that not the case?
Because we would need to be looking. The sky is so very vast, and our imaging equipment needs to look at such a small part in order to resolve the galaxies beyond our own.
