Well I think it is because Indonesian language is quite a neutral language, just like Dutch and German. All sounds in English spoken can be found in Indonesian language. Urdu and Bengali I also think is similar, but language like Vietnamese, Thai, and Chinese IMO is rather difficult for their native speakers to use English, except if they spend a lot of time in US or Britain.
Unlike India, Malaysia, Singapore, and Hongkong, we use Indonesian speaking mostly in our every day life, English is only used in professional work in written form. This make English speakers dont get local influence like how Hongkong, Singaporean, and Malaysian, despite Malaysian English I feel better than Hongkongers and Singaporean English since Malay language is rather more neutral than Mandarin. My sister for instant can speak English both in US and British accent despite she is educated in Indonesia fully and never live in Western countries ( only for short period of time like 1 week )
This is another English written song made by Indonesian and sung by Indonesian singers