Not enough space.
That's my problem.
I tend to have scenes that I absolutely love and want to include. So I put them in and then I have to go back and tear them out. And of course they're really not useful anywhere else. Well, they are, kinda, but really, they're so specific to the book ...
I've got too many ideas bubbling in my brain. Maybe I should write a Mega Book, like Diana G. and put ALL ideas into one book.
Nah. It's too much fun inventing new characters.