Our intuitions disagree. People, in my experience, are much more highly motivated to affect their own lives than to become slightly better at affecting the lives of distant (in space or time) un-seen others. The latter is abstract and personally irrelevant, the former is concrete and personally beneficial.

How many people spend thousands on personal growth workshops vs. spending money to research the best charities? I think there are many orders of magnitude there. On the other hand, getting the best charity right may make your charity 100x more efficient, while a personal growth workshop may only make you a few percent more efficient. But personal productivity is multiplied by everything you do, while only a small portion of your budget goes to charity. Multiply these out, and I think you'll see that the effect on improving individuals is much higher than on improving their charitable giving.