Companies with large, long-established brands can surf on that for a little while, but ultimately advertising works. If it didn’t, companies would drop it as soon as they could. I work with a company that does mail campaigns for businesses - especially restaurants. Even when they can demonstrate from the clients' own numbers a consistent net 2:1, 4:1 or even 6:1 ROI it can be hard to get them to maintain budgets. They really don’t like spending the money, but when they don’t maintain campaigns their numbers take a huge hit and they come running back.
Could Apple launch a new phone with a minimalist campaign, or Chevy skip a year of ads? Sure, but sales would almost certainly be significantly weaker, and almost certainly would result in lost net profits.
As far as profit margin, take a look at clothes sometime. The unit markup on that industry is enormous.