For that matter... why not just geocache?
Well, some people do have more than one hobby, and I'm looking to combine 2 of mine together. I am out of the house plenty, and geocaching is part of that, but I can't be out of the house all of the time, nor can I geocache ALL of the time. Add to that the fact that I can't play board games all of the time, nor can I spend every waking moment with my wife or family. Given these facts, I think there's plenty of room for some cross-hobby action, and if it were the other way around and I were going out for a day-long hike or weekend geocaching trip, you better believe that I would have a board game or 2 packed along with me.
I notice that many of the responses tend to lean towards the ideas behind Hasbro or Milton Bradly type games (Monopoly, Battleship, etc...) and while those games are certainly fun - particularly with kids, my other hobby of board gaming has opened my eyes to a huge world beyond what you can find at Wal-Mart or any other big chain store that sells toys and games. There are quite literally tens of thousands of board games out there with a plethora of various mechanics, gameplay, and strategy approaches. Some use dice to move a pawn, some use dice for combat, many don't use dice at all. Some involve moving around a track on a board, some involve creating the board with tiles as you play. If any of this sounds interesting to you, then please check out www.geekdo.com.