I think the author's perspective is skewed because he's living in Yogya, which is, and has been for a long time, the center of a large and prestigious culture.

I think the author's perspective is skewed because he's living in Yogya, which is, and has been for a long time, the center of a large and prestigious culture. Yogyakartans don't need to speak Indonesian unless they're dealing with the government. It's very different if your native language is only spoken by a small number of people and / or isn't very prestigious. Then there is, like you said, the capital, Jakarta, where non-Indonesian languages are only spoken at home (or not at all). And I know for a fact there are is at least one region - but there's probably more - where the local language has pretty much died out. Minahasans, from Northen Sulawesi, no longer speak Minahasan languages, they speak Indonesian.