They do it for the human interaction here on YA, just like you have done with this question. A google search would have shown you this question has been asked thousands of times.
With many questions, you are correct. However, a question like "Who was the backup center for the Celtics in 1968?" may take some searching and you may need to go through dozens of web pages in your search. Ask that same question on YA and within 24 hours, you have the exact answer, with no effort from several Celtic fans.
A student working on a paper may ask, "What were the causes of the Civil War?". The google result for that is totally overwhelming. On YA, a brief, clear paragraph that will suit the student's need may be obtained, if lucky.
Think of it this way. Google does not provide answers. Google provides information for a person to determine the answer themselves. On YA, a person tells you the answer directly, no thinking. It works like when you were a kid and you said "Mom, how do you spell Mississippi?" and Mom said "Look it up in the dictionary !!" Mom if she answered with the spelling was YA, the dictionary is google. Same concept.