So many reasons (in no particular order)... boyhood dreams, ambitions achieved, the view, the feeling, the technical interest, the freedom, navigation, the challenge(s), etc. etc. I suppose that like (I am told) golf is, you can never master it - there's always more to learn and explore.
I think that at the moment, as only low hours PPL, I get the most excitement and satisfaction from landing - particularly at an airfield I have not previously visited, and particularly if I do it well!
Andy