Hi,

 Possible causes include:

* the plants need an establishment period where they focus on new root development, not flowering and subsequent seed production. If that's the only reason, then next year you'll have lots of flowers.

* A soil test will show if the pH requirements of the plant have been met. Regulating the pH will result in the plant thriving.

*If someone sheared the plant back, then this year's flower buds may have been removed. Prune or pinch back the stems no later than the 4th of July.

 Best of luck!