As mentioned using a metonym makes the article more engaging by avoiding repetition. But I want to point out that it is often not the Capital per se that is being referenced but the city parliament is seated in.

For instance, the Netherlands’ parliament is based out of The Hague, so it would be odd to reference to Amsterdam (the capital) when referencing it’s government as there is no clear link with that city. Similarly, you don’t often see London referenced in this regard, more likely Westminster, an area within London.