Growing up as a kid in Algeria, you just accept the fact that you don't have the right to visit and see other places in the world; very depressing.
if u got 1.4b population and...er...lower gdp/capita... then its harder to convince people to let you in.....
Belarus, Cote d'Ivoire, Cuba, Djibouti, Ghana, Guinea, Iran, Kenya, Myanmar, Uganda, Vietnam.
Everything else is either visa on arrival or the same between the two (or worse for Singapore).
I'd like to see Cuba and Iran. Maybe Vietnam. Kenya, I've been to, although at the time the visa was granted at entry (though it was not free). And not all of the e-visas are free.
But in the grand scheme of things, my US passport makes it harder in four countries I would ever have an interest in going to unless there was something spectacular I don't know about. Seems like it's a pretty minor thing, not like it was in the early 90s when I needed a Taiwanese visa that required going to a consulate.
Pretty much all "rich country" citizen issues boil down to a handful of highly restrictive states and a few that have particular issues with the US government. It's not really limiting me the way that, say, an Indian passport would.
https://www.bbc.com/news/world-europe-66200194
https://www.bbc.com/news/world-europe-63747732
https://www.cnn.com/2023/07/14/europe/russia-lgbtq-rights-ge...
https://www.cnn.com/2022/12/05/europe/russia-lgbtq-propagand...
Honestly, I doubt anyone I know has ever heard of these Russian laws.
The company also has a useful database of all passports you can check for your own passports and see what countries you can enter visa-free.[2]
[1]: https://www.henleyglobal.com/newsroom/press-releases/2023-passport-index-global-mobility-q3
[2]: https://www.henleyglobal.com/passport-indexThey are rigging the results by not counting the new restrictions on UK citizens entering and operating within 27 EU countries, including the 5 countries they visit most: Spain, France, Italy, Greece, and Portugal.
No honest person would claim that the UK passport is equal to the Danish, Irish, or Dutch passport. Absurd.
I am not aware of even one country, anywhere in the world, that has made entry easier for UK citizens following Brexit. Certainly, nothing has happened over the past year to justify the UK rising in the ranks.
I have a UK passport but, even before Brexit, found it more pragmatic to travel on my Irish passport. British tourists have long had a somewhat tarnished reputation and, in some countries, resentments still linger from Britain's rather brutal past.
Since Brexit, over a million UK citizens have applied for and received Irish passports, giving them back the EU citizenship rights they had before Brexit.
So that's going to be some of the mobility decline for US travelers
In my case (Dutch passport): the Netherlands is a member of many inter-governmental organizations, regarded as trustworthy & often working to advance common goals. Longtime stable democracy, financial & (mostly) functional legal system. And thus travellers carrying a Dutch passport are welcomed in many places.
It's easy to see that for example socialist-leaning nations may not be 'liked' by the US (and vice versa, often for good reasons), and prefer to go their own way. I don't judge / have no beef with that. A sovereign state is just that.
But net result may well be that such a country takes part in fewer trade agreements, is a member of fewer 'country communities', and has less-friendly relations with some other countries.
And for example an assortment of African countries may be recovering from colonial history, or too busy with internal problems to focus much on international relations.
Again: no judgement here. It is what it is. But these things are exactly what tends to produce lower rankings. Rub some countries the wrong way, and find your citizens are less welcome there.