There are several possibilities why apple trees bloom but fail to set fruit:
- Apples are not self-fertile and need another apple tree or tree(s) of another different variety (or varieties) so the flowers can be pollinated (by bees, see #2.) and set fruit.
- Apple flowers rely on bees to carry the pollen from one variety to another so the flower(s) can be pollinated and the fruit can set and begin to grow. Both domestic honeybees and wild pollinators (bees, wasps)