I think going after all aggregators would have weakened the government position. The current approach forces Facebook to weigh the likelihood of other orgs getting onto FBs turf, once FB is onboard, the government can go after the others, one at a time. It works better via divide and rule vs having all providers presenting a united front and dropping Australia _en masse_ (which would have a high political cost, vs FB alone which doesn't have a lot of political capital)