One reason is because every silly keystroke is digitally recorded and archived before it is thrown away. Why not look at it first?
Search experts say that most of us start a web search with one or two words. Then, we scan the results, add another word, and so on, 'boiling the ocean' until we get what we want. Only two percent of us use the advanced search capability to make a short cut.
Whenever I drive into a crowded parking lot I drive closest to the door I want to enter, and start looking from there for a parking spot. My wife says, 'You've got to be crazy. Can't you see the lot is almost full?' I figure I will usually find a spot closer than if I had accepted the obvious places farther away.
Same with search. I trust the software. I want to exercise it by plugging in search terms that most exactly reflect what I want to find. I figure if there are 10 steps between the 'top' search term and the result I really want, why not start as close to step 10 as possible and then back off?