Match-fixing - why does it happen?

There is yet again an issue of match-fixing in cricket.

On SABC TV an announcer questioned why athletes get involved in such and questioned if the athletes are not loyal enough to South Africa.
In my opinion, the question of loyalty is just a little naive.
I believe that the issue is much deeper than what many people think.
In essence, 


According to Wikipedia, "In organized sports, match fixing occurs as a match is played to a completely or partially pre-determined result, violating the rules of the game and often the law. There is a variety of reasons for this, but the most common is in exchange for a payoff from gamblers. Players might also intentionally perform poorly to get an advantage in the future, such as a better draft pick, or an easier opponent in a playoff. A player might also play poorly to rig a handicap system.

Match fixing, when motivated by gambling, requires contacts (and normally money transfers) between gamblers, players, team officials, and/or referees. These contacts and transfer can sometimes be found, and lead to prosecution, by law or by the sports league(s). In contrast, losing for future advantages is internal to the team and very hard to prove. Often, substitutions made by the coach designed to deliberately increase the team's chances of losing (frequently by having one or more key players sit out, often using minimal or phantom injuries as a public excuse for doing this), rather than ordering the players actually on the field to intentionally underperform, were cited as the main factor in cases where this has been alleged.

Match fixing generally refers to fixing the final result of the game. Another form of match fixing, known as spot fixing, involves fixing small events within a match which can be gambled upon, but which are unlikely to prove decisive in determining the final result of the game."

In essence, it has everything to do with ethics, or the lack of the same.

An athlete who has ethics, will compete and only aim at a fair return. Such an athlete will not even consider taking more than his/her fair share.