A lot of commenters are completely overlooking the gender dynamic here. A husband earning much more than his wife is different than a wife earning much more than her husband.
If, as you imply, he feels emasculated by his wife earning more, that's his problem to solve with himself first. His wife shouldn't have to take the brunt of this on top of what is likely a high stress, high pressure career.
Sure -- but this dynamic is extremely well understood -- it's not like it's only every fifteenth man who would feel emasculated by this -- it's more like every other man.
Can you elaborate? Intuitively it feels you might be right, but every reason I can come up with myself I can also rationalize to the point that it shouldn't matter
This is just a phenomenon that has been studied by social scientists. Men who are earn less than their wives, or who are stay-at-home dads, are more likely to get divorced. You may say "well, they should just grow up and get right with God", and that may be true, but it is nevertheless a widely-observed phenomenon. It's the way the world is, although perhaps not the way the world should be.
The difference is that social scientists have studied gender dynamics and have observed that men who are out-earned by their wives are more likely to get divorced than when it's the other way around. I'm not saying that this is the way the world should be -- I'm just pointing out that this is a well understood phenomenon.