I have six blueberry bushes, four regular planted in a row in the same bed and two dwarf planted together. Two of the regular were planted at least six years ago and the other two about three. Only one of these bushes bears heavily, the rest hardly at all. I have not really pruned any of them much at all. THe dwarves were planted last year and one of those is bearing heavily, the other not.
Lane County Oregon blueberries
Thanks for your question! One factor is that the plants haven't been pruned much. That can result in heavy fruit set for a year, followed by very low fruit set. During the year of heavy fruit set, the plants put on very little new shoot growth, and that means sparse fruiting wood to set a crop the next year. Here are several links that may be helpful:
"A Grower's Guide to Pruning Highbush Blueberries" (video): https://media.oregonstate.edu/media/blueberrypruneenglish_ver2010.mp4/0_05v1qew6
"Growing Blueberries in Your Home Garden": https://catalog.extension.oregonstate.edu/sites/catalog/files/project/pdf/ec1304.pdf