Why do developers hate to write documentations? If not how do you document your code?

I was totally against writing documentation when I was younger but now I document every function in header file and every static one in source file. What I don't do is pollute function implementation with unnecessary comments. A few comments here and there are fine if something is ambiguous enough to require some explaining. I am doing it for myself because without it, when I stay away from the code even for a week, I am already confused and having hard time following my own insidious creations 😁.