Why on earth would this guy be taking donations when he is already a millionaire and can fund any projects he wants with his own money. I never liked this guy and think he is absolutely crazy. Just another rich person trying to protect the status quo.
He accepts donations because people send donations, it really is that simple.
Now why people donate to an already wealthy man - maybe his knowledge helped them in their life and they want to return the favor. However if you're considering a donation, please remember that there's other causes your money can go to - lifechanging surgeries of kids in 3rd world countries, orphans, research of uncurable illnesses, etc...
Peterson would gladly become even richer for his work, but he doesn't really NEED your money.