In all honesty - if I was an attractive woman.. why wouldn't I marry a rich guy in the US and spend the rest of my life living without a care in the world?

Because happiness isn't all about money? Because of the potential for someone to control and abuse you in that situation, for you to not be autonomous in your own major life decisions? Because there is still some financial insecurity when you sign a prenup and your husband could leave you for a younger model? Because it's embarrassing to be married to a rich douchebag? Because being objectified as a trophy is not most people's dream? Because many people want true love and happiness? Because women want sexual satisfaction in their lives too?

There are tons of other reasons.

Granted, I understand why some people use marriage as an "out" from awful situations, like dire poverty, and even why they become trophy wives if they have low self-esteem and don't feel they can do any better with their lives. People make all kinds of bad decisions (to the latter) and they make decisions out of various kinds of desperation (to the former). But you make it sound like it's the natural course of action for an attractive woman. Many attractive women actually want to marry for love, accomplish things, not be controlled by their husbands, etc.

Does Melania seem happy to you? She doesn't, to me. I would choose my own life over hers 1000x over.