Because of the prestige, power (and connections) it gives. All of these can be monetised later when high-profile jobs run out. For example, Tony Blair earned in the range of £150k per year as British Prime Minister. Now he charges up to £250k for a 90-minute speech and is believed to have earned over £20mln in the 3 years following his resignation.
Whatever is the truth in this matter it appears the damage has been done: http://www.abc.net.au/news/stories/2011/07/01/3258708.htm Now a new head of the IMF appointed, and his chances of office finished.
Guess, he is innocent after all, too bad he lost his fabulous job. His accuser is ugly bagger. http://www.nbcnewyork.com/news/local/Dominique-Strauss-Kahn-Charges-Dropped-Motion.html