Why do Indonesians drive on the left?

It sounds like a stupid question to ask if you live in Europe every day. Having lived in China, US, driving on the right side of the road is the normal thing to do for me. Until one day Mr. Aawaraa mentioned that when he first came to US, he would easily bumped into other person since he was used to walking on the left. Mrs. Aawaraa thus realized that there were quite some countries driving on the left. This became real experience when later visiting India, it was really very easy to walk on the wrong side of the road. Another visit to UK was also similar, cars running on the left side of the street is the first thing to remind you that you are in a different country. For me, another connection was also established: India is British colony, and that is why they both drive on the left.

This connection however troubled me a lot in my recent visit to Indonesia: Why do Indonesians drive on the left side of the road? I couldn't understand, because, because Dutch drives on the right! Indonesia was Dutch colony, but how come they do not follow the Dutch rule?

What makes this even more troubling is, nobody knows the answer. I kept asking everyone around, including some university professors, master students, nobody has any idea... I just can't understand, why do Indians follow their colonizer, while the Indonesians do not. That doesn't make sense to me, not at all.

Then I have to rely on my own research abilities, I have to do the research myself. A brief search connect me to this map, however, it doesn't answer my questions. It only give the history after 1858, and the Netherlands drove on the right, and Indonesia drive on the left since then.

My further findings are really interesting. In this website, it writes:
When the Dutch arrived in Indonesia in 1596, they brought along their habit of driving on the left. It wasn't until Napoleon conquered the Netherlands that the Dutch started driving on the right. Most of their colonies, however, remained on the left as did Indonesia and Suriname.

So, this is consistent with my previous connection: Indonesia did drive the same as their colonizer Dutch. What has changed is the Dutch rule. However, I couldn't find very reliable sources on the history of the change. It generally talking about it here,
The Netherlands drove on the left until Napoleon's time, but Dutch colonies (mostly) remained on the left as did Indonesia.

Reading more you will find, it is hard for a country to maintain left driving if your neighboring countries all drive on the right. The Netherlands being a small country in the middle of Germany and Belgium, even if it didn't change during Napoleon time, it would have to change later when most of the Europe drive on the right. Indonesia was able to stay on the left, is mostly because it is a country on islands. There are not much confusion of changing the side if you drive into a different country.

This may hold true also to India and UK. India has bordering countries, including Nepal, Bangladesh and Pakistan, all drive on the left till today. The Himalayas on the north minimizes the traffic almost to zero. UK sustains because of its being an island country. However, I heard that were complains about cars across the British tunnel can not be easily used in France. There might be one day this globalized world will move towards driving on one common side of the road.

The picture was taken in Dublin, Ireland in 2008. It was to remind pedestrians to look to the right for upcoming cars, definitely a sign for those people who come from the right side driving countries.