I'm Indonesian. Lots of people have Bahasa Indonesia as their first language, especially in the cities. Unless you go to the remote areas, you practically won't find people who can't speak Indonesian.

In fact, it's the use of regional languages like Sundanese which is diminishing. I could really feel the skill and the vocabulary range of even the native Sundanese are worse than 10-20 years ago. Lots of mixing with Indonesian vocabulary without knowing the Sundanese words.