Because billionaires are more often than egomaniacs and having your name be remembered is more important than the actual value of your charitable donations. We

Because billionaires are more often than egomaniacs and having your name be remembered is more important than the actual value of your charitable donations. We grew up in a world dotted with buildings and universities with the names of robber-barons like Carnegie, Vanderbilt and Rockefeller. Having your name carved into the stone of the building of a major institution means immortality (well, as long as the institution remains important) - directly sponsoring science might do more real good but it's not as good at sanitising your image or for being remembered long term, which are the real goals of most billionaires' philanthropy. People don't remember John D. Rockefeller for the money he pumped into eradicating hookworm, probably the single greatest thing he did for the world in his life - ending generations of sapped energy and cognitive impairment in the American South. People remember him because his name is on the buildings and colleges he funded.