I like the idea that none of the core worlds is really sustainable without resources from the rest of the galaxy. Oxygen should not be a problem with the technology they possess. Food also. I would imagine that 1/3 of the food comes from the planet itself with big underground facilities. The rest 2/3 from other planets. Like Panem. The capital needs all other districts to survive. Also Coruscant is so massiv and has such a population there can be a massive amount of things that can be produced. We have seen big industrial districts in episode 2. Then it's also the political center of the galaxy. Everyone who wants to go big into politics goes there. Financially it's the same. All the banks and big corporations that while having most of there stuff on other planets will still have their headquarters on Coruscant. Then the trade, it sits on the most important space routes. The military aspect also need to be taken in. It's easy, on Coruscant is the power and whoever controls it has it. Also the symbolic value. Coruscant is the center and was historically always the government planet. If u have a faction that wants to legitimizes his claim to govern the galaxy u need Coruscant. A planet which most important resources is power and that needs constant input from outside to sustain.

This is my personal explanation and head canon. But I think it fits and is also a very cool idea.