Indonesia is certainly the most neglected big power both in modern day and historically. It doesn't bother me so much as it surprises me that a nation of their prowess is neglected as much as they are. But if you look at how things are shaping with (1) ASEAN's potential playing a massive role and (2) globalization really advertising Indonesia on a noticeable + significant level more and more each year, you could argue that in 25-30 years time history will be "re-written."
Nevertheless, I'm trying to wrap my head around why that is. I think a big part of it is that they have always been really friendly with people. I mean, there has been A LOT of violence but Indonesia typically shies away from global events - or they have historically withstood them with little fuss. I'm not entirely certain but part of it could also be the "islander" culture where Indonesians are generally very happy where they are - colonial and wartime history created strong historical ties with the Dutch but that's about it - and thus have no reason to mingle in mass numbers overseas.
Locality has a lot to do with it. It's very hard to invade from one small landmass to another unless you are significantly technologically superior (and even then it's more difficult than normal) so it encouraged a different kind of diplomacy and empire building than somewhere like Europe did. Trade & Mergers and Splits rather than conquest are the drivers that tend to be at play in the history of the region. It's led the Indonesian area to be fairly much pacifists rather than warmongering.
They have an interesting relationship with Australia - they are the two main players in local affairs but their obvious cultural differences often lead to some strange interactions that don't always make sense to people from outside the area (or each other). The chances of either ever going to war with the other is practically zero as neither is aggressive by nature. If the US declared war on Indonesia that might change but frankly that's about as likely as me beating Brad Pitt in a list of the worlds most beautiful people at this point.