^Because you don't watch Supergirl?
Along similar lines...if there are infinite possible alternate universes, then there's potentially an alternate universe for any combination of people and/or events. It could be that alternate universes that just happen to have a strong coincidence of people, for example, despite drastically different historical events, are cosmologically "closer" and thus easier to travel between.But maybe there are different parameters for "closeness" between parallel realities, and similarity of sentient inhabitants carries more cosmological weight than similarity of material objects and events. Maybe there's even some sort of probabilistic bleed-through between universes that influences the same people to be born even when events go differently.