Plus, Manny was a politician last I checked, I don't know if he still is or not but it really was an important reason why he had that Mayweather fight as well, dude used all that money to get bigger and bigger in politics.
So, I am sure this fight will not probably happen but if they do have this fight I am sure the money reason would be for politics and not anything else, he probably has enough investments and savings to cover all the smaller expenses like salary and car washes and everything, those are easy stuff to pay for, when it comes to politics tho, paying your way in (bribing) always requires more and more money, the more you spend will result with more you further your career as a politician, which means he kinda "needs" money but not in the way you think.
Manny Pacquiao is still into politics. Currently a senator. It is possible that he still wants to continue fighting in order to finance his political ambitions. it is not a secret that he wanted to become a president one day (I hope it won't happen). But I cannot say that he is up into bribery or something. Pacman is a very religious and traditional guy. But who knows.
But hey. I don't think this fight is gonna happen. McGregor is already making big money like 8 digits per fight in mma. And McGregor can cherry pick all he wants. He can fight Mashvidal if it losses to Kamaru, or anybody which is less dangerous than the current champions.