First: It's hard for me to read big books. I can't understand why because I will read them anyway. But seeing a massive 700 pages or more book on my front scares me. Can you understand why? And explain to me? The biggest book I've ever read was and Harry Potter with 600 pages. Then there are several ones with 416 from Black Library. I've got only a handful books read with more than 500. I could count them with one hand.
Second: Why are the books getting bigger? Apart from a couple of ones most of the books which you could call Masterworks (and we can go with Gollancz Masterworks of SF or Fantasy) don't have more than 400 pages. (There are exceptions of course). Why are books getting bigger? Look at George RR Martin, Steven Erikson or Peter Hamilton... Look at the Brent Weeks, Robin Hobb, K J Parker, Tad Williams... Etc
Is bigger ... gooder?