Are you familiar with the term "black swan"? A unique, rare event that is impossible to predict. That's what Fan4stick was. Word of mouth was so bad that people were returning their tickets for Friday after hearing Thursday reports.
There was NO way Ghostbusters was ever doing those numbers, barring apocalyptic critical response.
Their biggest mistake was doubling down on making this a Paul Feig movie as opposed to a reboot/sequel to a beloved franchise. Thus, it performed like a Paul Feig movie, instead of the blockbuster it needed to be given the budget.