Peering into a webcam, her face intermittently frozen over an iffy Skype connection in Medellin, Colombia, Lizz Quain was explaining not long ago why she uprooted her 9-year-old twins almost a year and a half ago to travel the world.Ms. Quain, who is in her 40s, owned a children’s play cafe and preschool near Seattle before she renounced her American middle-class existence in August 2016, fed up with what she described as a stifling, consumerist culture.Once Donald J. Trump was elected president, she made a common liberal refrain — “If Trump wins, I’m leaving the country” — reality, deciding not...