Q.Why Are My Thornless Blackberry Plants Have Only 1-2 Canes?
I had a blackberry plant for a long time. It made new plants and I replanted them. But I never get more than 1-2 canes from each plant. This cane makes usually only 1 or 2 lateral branches. I get blackberries, even quite large but just a few on each plant. All blackberry plants that I see online are very bushy and have many canes, branches and clusters of berries. What am I doing wrong?

Certified GKH Gardening Expert
I would test, both, the soil fertility and drainage. Poor drainage, and poor fertility will lead to these issues, typically. Here are some articles that will help:
https://www.gardeningknowhow.com/garden-how-to/soil-fertilizers/testing-moisture-in-plants.htm
https://www.gardeningknowhow.com/garden-how-to/soil-fertilizers/testing-soil.htm
https://www.gardeningknowhow.com/garden-how-to/soil-fertilizers/soil-ph-plants.htm
https://www.gardeningknowhow.com/garden-how-to/soil-fertilizers/test-soil-for-pests-and-diseases.htm
https://www.gardeningknowhow.com/garden-how-to/soil-fertilizers/making-sure-soil-drains-well.htm