Because there are some things that the market just won't do effectively. Basic science that takes decades to pay off is a good example. Somebody has to understa

Because there are some things that the market just won't do effectively. Basic science that takes decades to pay off is a good example. Somebody has to understand the biology so that decades later someone else can build a product. Private foundations can pay for some of it - a lot of the green revolution was funded by the Rockefeller Foundation - but they don't have the resources of the federal government, and you're relying on the whim of a single family or individual. Government-funded basic research has worked out really well for the US.