Maybe you have never travelled to a poor country?
What percentage of Africans living in poverty, corruption, dysfunction do you think would like to migrate to Europe, the US or Canada? It's 'most'.
1/2 of Chinese would emigrate according to a few surveys [1].
Since everyone has the internet - they can now see that people elsewhere live in considerably higher material standards of living, why would they want to stay? Basically, family and culture ... but most people would trade that for a decent job and stable governance.
Yes - totally agree the solution is to help poor countries have some wealth, but what can we do to help? They mostly have systems of total corruption. Any real attempt to try to fix underlying problems would be utterly destroyed by leadership who wants to maintain their status. Either governmental or non-governmental.
Most African countries run on bribery. All the way up and down. So if a US Agency comes in and starts exposing this, how is the leadership going to react? With massive anti-American sentiment is how.
This is happening right now as China is greasing government figures to buy up land on the cheap. They're bringing in their own workers in lieu of hiring Africans. Why? Because they can, and they are paying off who they need to to keep it that way. [2
Finally - even if countries were wealthier - there would still be massive emigration.
Poland has a GDP/capita of about $14K US, but in PPP it's much higher. Poland is 'poor' for a rich country, but they are not poor. They have stuff. They have industry, they have regular clothes, housing, highways, governance that mostly resembles ours. None of it is UK/US standard ... but it's still pretty good. They are 'rich' compared to Nigerians, easily.
And yet, there's a massive exodus of Polish labour into other places, particularly the UK, which has caused calamity in Europe. That's a different kind of migration, because I think many Poles return at some point, but nevertheless, it's big.
So no, open borders would be a migration disaster by any stretch, even in some distant future where Central South American countries are hopefully much more 'caught up', it still can't work very well.
I think a NAFTA type arrangement for all of the Americas is within reason though: no visa requirement, and possibility of easy work for a few years, then apply for citizenship.
I think the fee for an H1 could be $1.5K a year. Maybe even a hint of a higher tax bracket, why not? $8K for an O1 sounds about right. You're supposed to be 'world class genius/talent' so that's not out of range.
[1] https://www.huffingtonpost.ca/2017/07/17/half-of-china-s-mil...
[2] https://www.brookings.edu/blog/africa-in-focus/2015/11/05/wh...