User blog comment:Hyperborean/"The House of Hades" – official expectations blog/@comment-96.235.6.20-20130430203341/@comment-4649443-20130508023234

They did. It's just that the first book was forced on them by their parents, so they didn't focus...then they returned to the series. Here, example:

Parent: Here's a book. It's called The Lightning Thief. Read it, or else!

Anon: But, Mom, I hate reading!

Parent: Well, you'd better get used to it.

5 Hours Later

Anon: I read the whole book! I'm free! Now to forget everything I read!

3 Months Later

Anon: Ooh, look, it's the second book in the series I read a few months ago! But...I forgot   the story of the first one...I even forgot the name of the characters! Well, never mind, I'll just read the second book already. Eff the first book.

7 Months Later

Anon: Bob is Percy's first stepfather, he was turned to stone in the first book

Awesome Person: No, his name was Gabe. Bob is the Titan Iapetus who got his memory erased inThe Sword of Hades.

The End

Moral: Anons, before reading the next book, review the ones before it.