1920 called, it wants its sexist opinion back
That's right, it's an old thing, but far older than you suggest. It goes back 100,000 years (for modern humans) and it's embedded in our DNA (going back millions of years). So it can't be sexist by definition because the reality of our World is that men and women are two different things. It's basic evolutionary biology. Some people can see the elephant in the room and some can't. We're not the same. Never have been, never will be.
It's not cheating for a successful man to enjoy the spoils of success. But it is cheating for a woman of a successful man to stray. Why is it different? Paternity. Biologically, a female is 100% certain of her maternity. That's not the case for men and the consequences of cheating to a male are far greater than to a female. If a female is provided for by a male, her job is to preserve his paternity. The male's job is to preserve his success. If a man extends his paternity to more females, it takes little to nothing away from his wife because he's still providing for her.
Now you're probably thinking, that's not how our social structures express themselves in modern society. I wouldn't disagree. I'm just pointing out the underlying drivers of our behaviour. It's not a coincidence to me that so many people are unhappy and at the same time are misaligned with their underlying biological expression. You keep a dog in the house and he's not going to be happy. He wants outside and to go for a walk. People are no different.
And this is a message to guys about commitment. Don't give away the farm you dummies.