Why do so many rich people lack table manners..?
The rich from the US of A are often newly rich and have no idea how to comport themselves. Moreover, since Americans in general lack skills in this regard and since-rich or not-they come from the same country, they are as likely to be slobs as the rest of us. Some of the rich may feel that they are above common manners because they are a special breed.
Table manners are down the list of proprieties in to-days culture. Most people don’t eat at dining tables anymore so they have adapted eating to suit sitting with plates on laps and eating junk food out of bags in the car. I don’t know any billionaires so I can’t comment on them and their eating habits. Money doesn’t automatically mean well bred or cultured today.