Lack of room.
I can see that the bushes are different. The ones that bore fruit last fall look dead, the other ones have redder looking, smooth bark and are putting out leaves right now.
My blackberries look pretty shot, too, except for one. I wonder if the winter was too hard on them. I was really hoping for more from them by now.
The one berry bush that's going to town and looks like it will be trouble to control is a yellow one a friend gave me from her garden.
I have Heritage raspberries as well. The other is Latham, I think.
Both are good varieties. I want to add the Kiwi Gold to my patch, too.