The guaranteed fight purse for Manny Pacquiao would be around $20 million and Thurman would take home around $8 million for the fight, Conor McGregor is a real super start in the sport and if Manny Pacquiao fights Conor that would be another $100 million fight day as Conor McGregor is a special talent who has the ability to pull huge audience irrespective of his boxing skills.
So you are indirectly saying that Manny needs the help of some heavyweight like Mayweather or McGregor to get to a figure of 1 million plus PPV buys. The last fight (Manny vs Thurman) got around 400,000 PPV buys and I guess that is the maximum that Manny can attract. Someone like Mayweather is needed to take the figures to 7 digits.