Let's start with the example: In the U.S., high-SES people used to smoke more than low-SES people until about 1965. Then the lines crossed, once, and they never crossed again. These days, there are many high-SES people that you don't have to tell about health risks: to them, smoking is prole. And who wants to be prole?
More generally, there are many behaviours that low-SES people show more frequently than low-SES people, and vice-versa. Why? Let me propose a two-step model. First, there is some initial reason why a certain behaviour is shown more often by low-SES people. Then, the behaviour becomes associated with being low SES. Then, the behaviour is reduced even more by high-SES people.
Smoking is, I think, a good example. Initially, high-SES people may have had access to better information, or have been better at processing the information, or had more self-control, or have put a higher value on health, or what have you, or all of the above. This created an initial smoking gap. This helped associate smoking with being prole. This, in turn, caused people who don't want to be seen as prole to smoke less.
In some cases, the reason for the initial reason could simply be chance.
The model implies that SES differences in smoking were easier to explain in terms of the psychological factors mentioned above (more self-control, etc.) in 1970 than today. Generalizing this is left as an exercise to the reader.