There's also the simple social factor which gets underestimated. I used to get worked up at work when people would ask questions about stuff I had written documentation about, until I understood that some folk just want that little social connection. They want a person to communicate something to them, whether they're concsiously aware of it or not.
It's also fairly common for people to just not be that good at searching for things. You have to word things in specific ways and learn what kind of sources to avoid and ones to trust. So asking people who do can be a huge timesaver.