I don't understand why not. B2B transfer should be a cheaper method of despositing, from the book's perspective, than just about any other method. Seemingly simple, easy and cheap way to get your money. Why would they want to discourage or disadvantage this? That said, I'm sure it's a some do/some don't situation.
let me give you the simple answer here why books don't like doing these.
books are here to make money, they get nothing for sending a players money to another book.
no they won't and they shouldn't.
a book to book transfer is a favor to the client, by no means is the book obliged to do this transfer. with neteller pulling out of the US market some books are doing more of these transfers then they feel comfortable doing just to accomodate some loyal players.
if a book gives you a reload bonus on a book to book transfer consider yourself very lucky or a big loser at that book that they'll do anything to get your cash in the door