I'd think it must be something to do with the location, Donna. Some trees are stimulated to bloom by day length or temperature, and others bloom when the weather gets dry after a rainy spring. My lychee tree has not bloomed at all this spring (no fruit, sadly) because we had an unusually wet winter this year - record rainfall for January. It's done this before, so I know it needs a dry period to stimulate its bloom cycle.
Is your locust tree by any chance in the middle of a lawn that gets regular watering? Can you possibly turn off the sprinklers that water the tree and give it a week or two of "drought" to see if this gets it to put out some buds? (the lawn in the shade of the tree probably won't suffer too badly . . . )
