The question quoted in the OP makes an assumption. Ads don’t show what people do. Ads show what’s worth it for the advertiser. Publications publish ads that they are paid for. Maybe ads are cheap in these publications and the luxury items offer the best deal. It’s worth it for everybody. The advertisers and magazines each make money, and everyone is happy.
Having enough people buy an item to offset the cost of advertising doesn’t mean that it’s a significant percentage of the population that are interested in these things.