Someone else can explain this philosophy better than I, but it goes something along the lines of...

"My value and power is based on my knowledge. I therefore shall not share it, for in doing so reduces my advantage."

'''Easy provocative answer:''' Most of our accidental knowledge and ideas (say 99.9%) cannot be used by ourselves
directly. But if we put some of 'em in a Wiki-system, there is a great chance that each participant gets more knowledge and ideas in his specific range of activities that s/he can use to their advantage (for a ''fraction of the cost'' of an alternative way of searching for that knowledge). And, by the way, transferring freely your accidental knowledge and ideas is a way to find new friends (''and make our fortune'':-) -- FridemarPache
 
See also: TheSecretOfPower, ImbalanceOfPower

Also: PeopleWhoDontNeedToKnow for an interesting related discussion