Because we can.
(Actually, I have a vague suspicion that the secondary reason I have for plane trips seeming so special - the first being that I love new places - is that I'm actually quite scared. I've read that a passion for peanut butter - I'm guilty of that too, btw - can be inspired by a slight intolerance. The body becomes addicted to the hormones released when it's consumed. I wonder if being in a plane is a bit like that for me. I am terrified of enclosed spaces. planes aren't that small but they are high and difficult to leave in a hurry. Adrenalin rush, maybe?)