For the very same reason why the wisest of the ancient and medieval rulers were patrons of science, even if the value of scientific discoveries was not immediately apparent at the time.

It is called enlightenment and the discovery of knowledge. Otherwise, we would still have been running around with pitchforks and flaming torches, waging crusades in the name of one deity or another.

Besides, humans spend $50 billion or – equally arguably much more – killing or trying to kill each other. If that gets spent on new discoveries and knowledge, it becomes apparent that the $50 billion investment into science is a substantially better value proposition.