The most likely explanation is poor pollination, especially since the fruit is dropping soon after bloom. The flowers need to be visited by bees to be pollinated. Blueberries will set fruit even if there are no other blueberries around but the number of seeds and the size of the fruit is reduced. If the weather is poor for bees during bloom, if it is cold or rainy this will also reduce pollination. We are seeing a significant drop in commercial blueberry fields here in Michigan as well. The weather after bloom during early fruit growth also influences the amount of drop we see. Bumble bees are the best pollinators for blueberries and some varieties are more attractive than others to the bees.

Hi,
I agree with Mark that it is likely poor pollination. There is a cultivar named Draper that drops fruit due to an assumed calcium deficiency in the fruit of that particular cultivar but unless the blueberries you are growing are Draper, this would not apply. Best wishes.