Do you realize how difficult it is to move from one country to another? It's expensive as hell, and if you're a US citizen you still owe taxes on money you make while living abroad.
speaking as someone married to an American who migrated to my country.. the cost of renouncing your citizenship is far cheaper than the backward arse tax system that applies to US citizens regardless where they live, and the need to pay someone to do your taxes for you even if you owe nothing.
Once you get citizenship elsewhere (if you can) I'd recommend renounce US on sheer economic grounds alone
Primarily because it's really difficult to move countries. Even when an other country is "better", by whatever metric you may choose, the high switching cost makes the move worse for individuals unless staying in a country is really really bad. That threshold is typically when subsistence in the country of origin becomes untenable, often due to war or famine.
Half the population has less than 1000 bucks in savings and doesn't have a degree like an MD that would bump them to the top of the list as far as citizenship elsewhere. How do you propose people make this happen? The people who are most disadvantaged are those who would have the hardest time doing so.