"But when asked what aspects have the most negative impact on work-life balance, work emails ranked rather low at 18 percent—topping the list were bad bosses, working after hours, and employers being inflexible about vacation."
Ah, the article is pretending that answering emails after hours isn't working after hours. They're the same thing, because thought and communication about details of work equals work. Bad bosses will tend to email after hours as well. Employers not respecting the majority of their employee's time (which is spent outside of work) is also closely related to being "inflexible" (not respecting the contract) about vacation. I think the article could have easily said that working conditions and labor rights in the US are extremely poor rather than pretend there is something magical about answering emails after hours.