My brother-in-law Ken Elder has come up with the reasons why tennis is such a great game. 

1. You don’t need a lot of other people to play - only one other person.
2. You don’t need to use modified rules - the professional rules are the only rules.
3. Tennis is free in the summer.
4. It is an outdoor activity, perfect for lovely days. It can be played even if the weather is not "perfect"
5. After you get better at it, there is plenty of action and exercise.
6. The risk of injury is the almost the same as walking down the street - nil.
7. The required equipment is cheap - almost nil if you spread the cost out per hour of tennis.
8. It is a non-contact sport, so anger is at a minimum.
9. It can be a non-competitive sport if desired - you can just hit balls back and forth for hours without keeping score - this is fun (much more fun than playing catch with a baseball) and there are no winners or losers; and it is actually better exercise than playing games since the ball is kept in play even though it may be slightly past the lines, and less time is spent getting ready for serves and changing sides.
10. Size does not matter - a small person can beat a large one
11. Tennis players are generally polite and good sports - they don’t cheat and don’t want points they haven’t earned
12. Tennis players generally do not drink much (except water) unlike players in some other sports where drinking seems to be a large part of the game (baseball, curling to mention a couple)
13. Tennis is one of the few professional sports that women can earn big money playing.
14. Maria Sharapova – enough said. (She made more money than Roger Federer in 2007, 24 million off the court – not including prize money).