Nitpick: It would be more correct to say that FB collects GST for the Australian Tax Office. In an accounting sense only consumers actually pay GST.
Also worth pointing out that FB’s tax bill in Australia is pretty minimal (rightly or wrongly). The tax on these payments could easily end up being worth more than Facebook’s tax bill in Australia.
Actually if you think of these measures as a creative way around US strong arming on a digital services tax they make a lot more sense despite the legislation itself being a weird mess.