It sounds like the dwarfs trees are complacent, as you should have had flowers and fruit from dwarf trees in 2-3 years from planting 2 year old plants .
The possible cure sounds unconventional.
It sounds strange but consider striking the trees in the Spring with a baseball bat, not enough to damage, but enough for them to seek replacement flowers/fruit.
Strike the trees above the graft on the fruiting branch that you are trying to stimulate.
Doubt me ? -fine. Then just try it on half the trees .
I have expierienced this , myself.
No doubts here, I am aware of stress related improved production. Tend to forget about it though. We have had flowers, but for some of them, the Missouri cool spring/frost could be an explanation.
One or two trees had some very small fruit - pencil eraser size. I have assumed that the drought we had two summers back did damage that hasn’t been offset yet. I know that the trees didn’t get as much water as they should have.
The wild blackberries used to be very prolific and produced big juicy berries. They haven’t recovered either. Only a handful to eat this year. The other issue is they are all too close to the walnut tree. Hubby was not aware (me either)of that effect.
I mentally kick myself now and then for not double checking, but he’s so knowledgeable, I just assumed he would know the best place to plant them. We are in the process of planting a few others in the back yard well away from the walnut trees.
Front yard so far has killed all the trees except what was already here. Used to be part of a tiff cut, and refurbishment continues. Thanks for the reminder, I’ll try to remember it come spring.