The ADD Narrator

I've started The Forgotten Garden by Kate Morton. I'm 66 pages in and the book has yet to settle on a single timeline or protagonist. Each chapter (and the chapters aren't particularly long) is from a new point of view, in a different year, and sometimes in a different city. They all follow the narrative of an abandoned child, but it skips around a lot.

We've all read these books, or heard someone say, "It was hard to get into because it kept jumping around and it took a long time to get attached to a character, but once I got into it it was great."

But I'm annoyed. It's like the narrator can't make up her mind about who to follow or which era she wants to be in. It's like the narrator has ADD. Is it 1913? 1930? 1975? 2005? Is it from the point of view of Nell, Cassandra, Hugh?

I understand that there is a mystery with this abandoned child, and skipping around gives us a broad picture of the situation while also giving us tiny clues about the mystery. But it feels like the narrator is dangling the mystery in front of my face, singing, "Nahnah nahnah nahhh nahhh. You can't get it." Or that the author doesn't trust herself to hook the reader from the beginning, and so each chapter she has to try to hook us again.

I understand there is a mystery and that I won't get all the details until the end. Now let's move on with the story.

You can probably tell I'm aggravated. But this isn't all to say the book is bad. I'm still reading it, after all. I'm just wondering...what does a story gain by jumping around, character to character and setting to setting? What are the pros of this story-telling device? What would lead an author to make this choice?

Thoughts, oh dear readers?