According to Sydney Morning Herald, it's a financial decision as they're losing millions of dollars.
[COLOR=#000000][FONT=Arial]Indonesia AirAsia X reported a first-quarter loss of $US4.6 million, down from $US9.4 million the prior year, based on its fleet of two aircraft....[/FONT][/COLOR]
Full story here:
http://www.smh.com.au/business/aviation/indonesia-airasia-x-cancels-flights-from-sydney-and-melbourne-to-bali-20160602-gpahjk.html