Question

why would a researcher use a secondary source instead of a primary source when analyzing historical event

Answer 1

to learn frim the conclusions of many other experts on the event

Answer 2

Because a primary resource would be an interview of someone in that event or their diary or something they wrote about that event. If you couldnt find anything, you would have to use the secondary source, a book or article written about that event but the author wasnt in it or there