Certified GKH Gardening Expert
This could have happened for many reason. Stress to the tree is the most common, but a fungus may have also attacked the leaf buds s or it may have been thrips that attacked the leaf buds. Since the tree was obviously under stress of some kind, it would have aborted its fruit in order to try to save itself.
If you can, have a tree professional look at it. These problems need a visual consultation to determine the root cause. If this is not possible, the best you can do is to make sure the tree is getting enough water and nutrients and to treat it with a pesticide and a fungicide. This would take care of the most likely issues causing this.