One of the reasons for Princeton's lower rank could be that it is a smaller school. Plus, it raises a disproportionate amount from alumni as opposed to other institutions with large corporate donations.

Look around. You won't see any Rolls-Royces pulling up in front.

Harvard and Stanford are always close to the top.

These are large research institutions, and a lot of these very big gifts go toward supplying infrastructure for, and paying for things like, medical research.

In the short run, it's more efficient to raise a small number of large gifts.