McD's and Coke are popular because people really want what they sell. It's not just a psychological thing, like everyone is a mindless zombie brainwashed by Ronald McDonald. They don't like it because they've been told to like it (if anything, it's the opposite these days), they like it because it's convenient and it has a ton of sugar and other addictive additives in it. People like both convenience and sugar; that's not a secret.
It's the same thing musically (though admittedly there is a bit more, not a huge amount more, of cultural influence here); there is a formula for music that most people find really satisfying. The record companies have software that analyzes songs and scores against the common patterns that produce hits. Of course, the business of music is about more than just the music, it's about the whole package.
People love cocaine too. It doesn't mean you have their best interests at heart in selling it to them. Modern commercial pop music, like junk fast food, is the product of a profit-driven corporation using psychology and focus group research to push your pleasure buttons without actually providing you with any nourishment.
The worst thing about both kinds of products is that they destroy local diversity and teach people to consume things that are worthless at best and actively harmful at their worst.
The issue wasn't whether Coke and McDonald's care about their consumers' health. It was simply that there is more to these brands than marketing. They're providing a product people really like. It is like cocaine. There is substance to the desire, which doesn't mean that its a morally or ethically justified desire, but means that it's not imaginary and it's not simply the product of emotional or psychological manipulation.
Do people want to do drugs as much as possible? Yes. Do people want to pretend that candy is normal food and eat candy for every meal? Yes. Coke and McDonald's are supplying the latter demand. It doesn't absolve them of responsibility and it doesn't mean they're not manipulative or dishonest. It just means that there is a real, physiological desire backing their products that's not artificially created by cartoon clowns or polar bears.
McDonalds contains objectively less nutrition than better foods, as well as objectively more addictive and potentially harmful additives (sugar, etc.). Today's stamped-out low-effort all-sounds-the-same pop contains objectively less novelty or information than, say, Bowie or the Beatles.
