I think a lot of artists create art to impress themselves, to look at something they made, and say 'I did this'.

All artists, even those who don't think that they are artists (because everyone is an artist), create to impress themselves. If they don't like it, they throw it away, trash it, destroy it, erase it, paint over it, just... get rid of what they don't like.

There are myriad reasons for creating art: money, fame, sharing of pleasure, political statements, etc., and the list goes on. In 2018, a study claimed an age of 64,000 years for the oldest examples of non-figurative cave art in the Iberian Peninsula. Represented by three red non-figurative symbols found in the caves of Maltravieso, Ardales and La Pasiega, Spain, these predate the arrival of modern humans to Europe by at least 20,000 years and thus must have been made by Neanderthals rather than modern humans. In December 2019, figurative cave paintings depicting pig hunting in the Maros-Pangkep karst in Sulawesi were estimated to be at least 43,900 years old. The finding was noted to be the oldest pictorial record of storytelling and the earliest figurative artwork in the world.

Why did these creatures (Neanderthals as well as humans) put them there?

Does it matter? Does it matter WHY David Hamilton took pictures of pretty litte girls? He did. And I like artwork. (Most of it.)