What's the "most desirable passport" depends on how many want to get citizenship to the country issuing it (which for the US is quite a lot), not on how other countries receive it's owners.
You're right that for the US it's a lot, though in my experience that's just because Hollywood is the best marketing agency on the planet, not because people make a well-reasoned decision on where to live.
I spent two years all over Latin America, and have now been in West Africa for 6 months. I meet people every single day that say they want to live in America. When I ask why, they say "because life is perfect there. Everyone has lots of money. Life is easy. There is no disease. There is no poverty. Everyone has lots of food. Everyone has a huge house with a beach view." etc.
When I explain that there are homeless people, people that lose their jobs, and people who struggle to make ends meet while working huge hours, people are completely disbelieving. They think I'm lying, because the TV told them otherwise, and of course people believe the TV more than some random guy.
When I suggest there are tons of other great countries (Australia, Canada, Scandinavian countries, etc.) they could live, they just shrug and say "I want America".
Hollywood has done a very good job of marketing America, but like all marketing, a lot of it is smoke and mirrors.
Well, that's one reason.
Another reason is plain business opportunities, and an (often misinformed, depending on the industry) idea that it's easy to make it big, money-wise in America. In some fields, of course, this is truer than others.
Of course Americans also overestimate the degree to which other people in the world want to get into America -- judging from pre-WWII immigration from rural Europe (which most of it was), or from modern-day immigration for developing countries.
People from already developed countries (e.g. western Europe, Japan, Australia, Canada, etc.) don't particularly care.
She literally had the idea, the UK was all quaint little villages with roads made of gold populated by Hugh Grant types.
I was saying there are homeless people in London, and he refused to believe me. After a lot of talking around, he said.. "oh, yeah, but they're black, aren't they".
He refused to believe there are white homeless people in London.
This isn't a list of most desirable countries to live in.
It's also a standard way to refer of holding a citizenship (having a passport of X country).
Besides, most Americans don't care about traveling and working abroad in the first place...
Still a valuable ranking, but it's a very specific one for a very specific type of person.