Gosh, my reasons seem so simple.
I do it because I enjoy the simple pleasure of finding coins in the ground. There's not really a reason per se... it's just nice to be by myself, and disconnect from the world for a little while. It's fun to think I know what I've found, but never be absolutely sure. The thrill of the surprise... I mainly do coinshooting, and old coins aren't even what I'm looking for, because despite the fact that I live - literally - on the Treasure Coast of Florida, my luck finding things more valuable than a quarter is atrocious. I had the best detector on the market, interviewed with all the old salts who know where to go and had found countless gold and silver coins, hunting the same spots they hunt... knowing the beach, and when and where... spend days and weeks and months hunting myself senseless... and what do I find? I find that if I hand my detector to my (then) girlfriend's 9 year old daughter when my arm is about to fall off after swinging the damned thing for hours, she finds gold within minutes. Meanwhile, I find... jack. That was eight years ago. Since then, I gave up worrying about finding anything "worthwhile". Now it's about the pleasure of doing it, and the little thrill I get from discovering what I have found. Even if it is usually a penny, nickel, dime or quarter. After all... if it's not fun, what are you doing it for?