I wouldn't describe Mack as affordable. These days there's essentially no daylight between them and say Intamin or B&M in terms of price.
B&M have been on the radar of Australian parks for quite some time now. They pitched for Rivals and have been on the list for AA's "billboard coaster" replacement. Price might have been a factor in the past but it isn't why we haven't seen one here yet.
Not entirely sure the criteria "must please enthusiasts" and "will have a significant impact on attendance and revenue" are actually different. Certainly the attractions our parks have built in the past decade or two that didn't please enthusiasts also didn't have a lasting impact on profitability, and conversely those that are beloved did. Scooby, Superman, Rivals versus Motocoaster, Doomsday or Buzzsaw... there's a reason our parks are happily dropping $30+ million on great coasters now.