To add some more detail regarding the new capital, Jakarta has some structural governance problems in the sense that it's very hard to improve infrastructure improve / stop the sinking of the city (mostly caused from over reliance on ground water pumping and permitting corruption / bad river management). Those problems might never be solved.

And separate of it's economic power it remains a center of power where the city mayor/governor always becomes a major national political figure.

Indonesia is actually a plurality of distinct island cultures, but with Jakarta, Java and Javanese culture sits at the top of the national political hierarchy. (Not to mention a sort of internal Javanese colonialism similar to the USSR).

The new capital could be part of dismantling some of the legacy internal Javanese power structures.

(To add a further detail re. Java vs. Indonesia, because of the mercator projection it's hard to see how big Indonesia is. It would stretch from Maine, past California almost to Anchorage).

New capitals also help prevent revolutions and uprisings. It's a lot easier to have a government that's insulated from the unrest of the masses, when everyone in its capital is loyal to it.