They're building a showcase city a thousand kilometers away in a different island as the new capital, but they're not relocating the 20+ million who live in Jakarta.

If they relocate the govt and companies paying salaries to those 20M, won't they also move there?

They are relocating the government. The private companies weren’t invited. This is like how Burma moved its capital from Rangoon to Nay Pyi Taw, Rangoon is still the commercial capital if Burma.

The other examples I would reach for are Côte d'Ivoire moving its capital from Abidjan to Yamoussoukro in 1983, or Nigeria moving from Lagos to Abuja in 1991. In both cases, the old capital is still far and away the largest city in the country, like 10× the new capital city.

> Nigeria moving from Lagos to Abuja in 1991

By comparison, since 2020 the Lagos population grew by more than the entire population of Abuja.

That's it: 20 million helpless people are going to move like sheep because shepherds are moving to another place.

I’m sure some will move, but that number is going to be closer to 0 than 20M

Jakartan here, will never move even if the whole city get flooded (more than it has been). I'll probably get a houseboat and settle down.

More realistically, Northern Jakarta is sinking, but the Southern part (and the suburbs/exurbs in the surrounding area) are still going to be okay and Jabodetabek will still be home to millions.