Blackberry plants won’t produce any fruit
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.
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.