Certified GKH Gardening Expert
The most common reason for irises failing to bloom is overcrowding. Dividing and transplanting them usually helps. In addition, it can be attributed to poor pollination. Try to entice pollinators (bees, butterflies, etc.) to the area with brightly colored flowers.
Here is an article that you may find helpful: https://www.gardeningknowhow.com/ornamental/bulbs/iris/dividing-transplanting-iris.htm