Laura McKenna points to the data showing that less educated whites are actually living shorter lives than before, and asks why Hispanics are doing so well. Here's the chart:
One possible answer is the Latino health paradox. For years researchers have noted that recent immigrants--precisely those without a high school degree in the chart above--from Latin America have better health outcomes than virtually anyone else. There are a variety of potential reasons. Immigrants tend to be healthier because that is required for migration; those who are less healthy are less likely to migrate in the first place. Diets tend to be better, with less processed foods (though sadly that is changing across Latin America).
It's reasonable to argue, then, that the high rate of Latin American migration since the 1990s served to improve life expectancy numbers (by, for example, having lower rates of infant mortality). As the rate of migration slows, as is happening now, we would expect the difference between Hispanics and other groups to narrow because acculturation and assimilation gradually lead people to take on the same bad habits as native-born Americans (both white and black).