They are 20 years old and never produced any fruit. I've cut them down a few times but nothing ever buds. My wild berries do just fine.
Blackberry Plants Won’t Produce Any Fruit
Certified GKH Gardening Expert
There can be many reasons and the fact that you have never produced fruit is concerning.
I would recommend a soil test. This is the only way to determine if it's an issue in the soil.
Here is a great article to help you start pinpointing and eliminating the cause.