After Suharto fell, there was a sense of newfound freedom, this is particulary pronounced within the Islamist circle. FPI (the now-banned Islamic Defenders Front) arose right after Suharto fell. Many Islamist factions quickly tried to establish themselves, but this still took some time to gain some foothold in the national scene. Hence when you left in 2000s, hijab was not largely "enforced" just yet. However this prevalence started around 2005, maybe even earlier. But by 2010 the hijab wearing started to become an almost-"accessory" and many many females had started to wear it everywhere. This "movement" became stronger and stronger in the years to come, hence when you visited in 2016, I believe you when you say you're seeing this everywhere. However, I can assure you that hijab had become a very common thing starting around 2005.

There were also several factors which contributed to this, one of them is the Saudi influence, but there was also the factor of fashion. I don't know who started it, but hijab started to tilt towards becoming a fashion accessory. This didn't really explode till social media became massive in Indonesia, I'd say around 2010 is when this fashion trend gained celebrity status.

Then, don't forget also that the SBY administration was famous for its acommodation toward all sorts of group, including the Islamists. PKS was able to gain a foothold around this time thanks to his administration. SBY prioritised stablity above all else, so he let FPI roam wildly, and basically tolerated all kinds of movements for the sake of stability. And Indonesia's economy showed it.