Why? Go read some more about Harrison "Jack" Schmitt, who was on the Moon with Gene Cernan. Having a geologist on the moon enabled spotting things, making judgements, and then following up on the spot. Sending a scientist who can also pilot (and Schmitt was damned good) rather than only having military pilots changes the game as far as the science return.
I wonder if with AI advances though, we can have robots that are 'damned good' pilots that can also spot things.
(The judgements would need to be made back on Earth though, admittedly, with speed of light lag as an annoying factor.)
As for me knowing about this... I have more perspective than most people, but it all comes from listening to scientists, who are the ones with knowledge of the science gains. I wish they had a bit more voice than they do.
At its peak NASA used 4.41% of the federal budget. In 2014 it was 0.5%. We can afford to do more and as we know from experience the payoff is worth the expense.