Why do developers hate writing documentation? Is it bad tools? Lack of incentives? Why?

I am puzzled by this… There is nothing like good documentation to understand how systems works. Yet developers are SO reluctant to write it. Why?

Help me understand please!

My guess is that there is not a single documentation tool designed SPECIFICALLY for developers. General-purpose wiki's are clunky and lack understanding of the code, convenient integrated tools. Am I wrong?