It's important for readers to understand how is because, when you write a story, or a school report, if you don't make some sort of suspense, people are going to get bored, or lost. Readers also should know why writers create suspense because, it's always a good idea sometimes, to stop yourself, and say, "Why did this happen"? Asking why helps you to understand, and visualize what's going on in the peice of writing.
That's all I got. Hope this helped!!