My blackberry bushes produced plenty of berries last year. This year the vines are bigger but there were never any blooms. I trimmed back the branches that bloomed last year and turned brown. I have now been told that there should have been branches last year without blooms but there were not any. This year I have plenty of branches but not a single bloom or berry.
No Blooms on Blackberry Bush
Certified GKH Gardening Expert
There could be a few reasons. Environmental, insects, disease or pruning.
You may want to do a soil test to really know what may be either missing from the soil or if to much Nitrogen is an issue.
Here are a few links for you that should help you pinpoint the issue.