What makes golf a rich mans game?

The equipment is expensive, greens fees are expensive, and many golf courses in the USA are part of a country club, with very expensive membership rates.

First, because golf clubs are requires relatively high investments in land, equipments, maintenance of grass, etc.

Second, because the equipment to play golf is not cheap.

Third, because this sport requires qualities such as concentration, focus, etc, that rich people practice daily.

Fourth, because it enables to socialize and talk "business" while palying a game.

Hope my answer is large enough :-)

Golf is probably the only sport where you have to spend money everytime you play. But if you love the game it doesn't matter.

Plus you can find way to save a lot of money playing.

Check out sites like this one Golf Discounts Online 

Golf courses require lots of land.  This in turn means that in places where land is expensive... the courses need to charge accordingly to make back their money.  And in places where snow shortens the season it is even harder for courses to be profitable.    So in the end it is an expensive sport -- and in places like Japan where land is really scarce you can imagine how expensive/elite it would be there.