mid-books crisis

Mickyd queried me whether I'd finished So Yesterday and I'm admitting I'm having a mid-books crisis. I get to the middle of the book and I get stuck and start something else. Mainly a YA problem at the moment. (Tim Winton's The Turning I've stopped reading a few stories short of the end because I don't want it to be over too quickly.) A book I've just got stuck in has a great start but our heroine's been stuck on a plateau for sometime and it looks like she'll be there for a while. Is this just a problem for me or are authors and editors forgetting the middles of books. Great starts but loose rambling middles. The editing finger itches as interest wanes. But perhaps YA readers don't want to finish books too quick and I'm out of step.