Why do some people like to travel to resort cities only, like Cancún or Cozumel?

I love traveling, but it's to explore other countries -- the way of living, famous landmarks, the food -- so resort cities aren't for me. I know people who make $200,000+ annually, and the only places they go to are Cozumel, Bahamas, and other resort destinations on cruises. On the other hand, I'm by no means rich, but I've travelled to Germany, France, England, Italy, and Korea, and am hoping to explore other countries soon. Sunbathing at the beach isn't as intriguing as exploring a new place and seeing how people live and the history behind it.
Why do some people like to travel to resort cities only, like Cancún or Cozumel?
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